SOUTHERN Co GAS (GAS) 10-Q4 Nov 212021 Q3 Quarterly reportFinancial data

Company Profile

Cover Page

Cover Page	9 Months Ended
Cover Page	Sep. 30, 2021shares
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	1-3526
Entity Registrant Name	The Southern Company
Entity Tax Identification Number	58-0690070
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	30 Ivan Allen Jr. Boulevard, N.W.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30308
City Area Code	404
Local Phone Number	506-5000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	1,059,803,931
Entity Central Index Key	0000092122
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Common Stock, par value $5 per share
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $5 per share
Trading Symbol	SO
Security Exchange Name	NYSE
Series 2016A 5.25% Junior Subordinated Notes due 2076
Document Information [Line Items]
Title of 12(b) Security	Series 2016A 5.25% Junior Subordinated Notes due 2076
Trading Symbol	SOJB
Security Exchange Name	NYSE
Series 2017B 5.25% Junior Subordinated Notes due 2077
Document Information [Line Items]
Title of 12(b) Security	Series 2017B 5.25% Junior Subordinated Notes due 2077
Trading Symbol	SOJC
Security Exchange Name	NYSE
2019 Series A Corporate Units
Document Information [Line Items]
Title of 12(b) Security	2019 Series A Corporate Units
Trading Symbol	SOLN
Security Exchange Name	NYSE
Series 2020A 4.95% Junior Subordinated Notes due 2080
Document Information [Line Items]
Title of 12(b) Security	Series 2020A 4.95% Junior Subordinated Notes due 2080
Trading Symbol	SOJD
Security Exchange Name	NYSE
Series 2020C 4.20% Junior Subordinated Notes due 2060
Document Information [Line Items]
Title of 12(b) Security	Series 2020C 4.20% Junior Subordinated Notes due 2060
Trading Symbol	SOJE
Security Exchange Name	NYSE
Series 2021B 1.875% Fixed-to-Fixed Reset Rate Junior Subordinated Notes due 2081
Document Information [Line Items]
Title of 12(b) Security	Series 2021B 1.875% Fixed-to-Fixed Reset Rate Junior Subordinated Notes due 2081
Trading Symbol	SO 81
Security Exchange Name	NYSE
ALABAMA POWER CO
Document Information [Line Items]
Entity File Number	1-3164
Entity Registrant Name	Alabama Power Company
Entity Tax Identification Number	63-0004250
Entity Incorporation, State or Country Code	AL
Entity Address, Address Line One	600 North 18th Street
Entity Address, City or Town	Birmingham
Entity Address, State or Province	AL
Entity Address, Postal Zip Code	35203
City Area Code	205
Local Phone Number	257-1000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	30,537,500
Entity Central Index Key	0000003153
ALABAMA POWER CO \| 5.00% Series Class A Preferred Stock
Document Information [Line Items]
Title of 12(b) Security	5.00% Series Class A Preferred Stock
Trading Symbol	ALP PR Q
Security Exchange Name	NYSE
GEORGIA POWER CO
Document Information [Line Items]
Entity File Number	1-6468
Entity Registrant Name	Georgia Power Company
Entity Tax Identification Number	58-0257110
Entity Incorporation, State or Country Code	GA
Entity Address, Address Line One	241 Ralph McGill Boulevard, N.E.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30308
City Area Code	404
Local Phone Number	506-6526
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	9,261,500
Entity Central Index Key	0000041091
GEORGIA POWER CO \| Series 2017A 5.00% Junior Subordinated Notes due 2077
Document Information [Line Items]
Title of 12(b) Security	Series 2017A 5.00% Junior Subordinated Notes due 2077
Trading Symbol	GPJA
Security Exchange Name	NYSE
MISSISSIPPI POWER CO
Document Information [Line Items]
Entity File Number	001-11229
Entity Registrant Name	Mississippi Power Company
Entity Tax Identification Number	64-0205820
Entity Incorporation, State or Country Code	MS
Entity Address, Address Line One	2992 West Beach Boulevard
Entity Address, City or Town	Gulfport
Entity Address, State or Province	MS
Entity Address, Postal Zip Code	39501
City Area Code	228
Local Phone Number	864-1211
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	1,121,000
Entity Central Index Key	0000066904
SOUTHERN POWER CO
Document Information [Line Items]
Entity File Number	001-37803
Entity Registrant Name	Southern Power Company
Entity Tax Identification Number	58-2598670
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	30 Ivan Allen Jr. Boulevard, N.W.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30308
City Area Code	404
Local Phone Number	506-5000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	1,000
Entity Central Index Key	0001160661
SOUTHERN POWER CO \| Series 2016A 1.000% Senior Notes due 2022
Document Information [Line Items]
Title of 12(b) Security	Series 2016A 1.000% Senior Notes due 2022
Trading Symbol	SO/22B
Security Exchange Name	NYSE
SOUTHERN POWER CO \| Series 2016B 1.850% Senior Notes due 2026
Document Information [Line Items]
Title of 12(b) Security	Series 2016B 1.850% Senior Notes due 2026
Trading Symbol	SO/26A
Security Exchange Name	NYSE
SOUTHERN Co GAS
Document Information [Line Items]
Entity File Number	1-14174
Entity Registrant Name	Southern Company Gas
Entity Tax Identification Number	58-2210952
Entity Incorporation, State or Country Code	GA
Entity Address, Address Line One	Ten Peachtree Place, N.E.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30309
City Area Code	404
Local Phone Number	584-4000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	100
Entity Central Index Key	0001004155

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Revenues:
Operating revenues	$ 6,238	$ 5,620	$ 17,346	$ 15,258
Operating Expenses:
Other operations and maintenance	1,446	1,286	4,257	3,785
Depreciation and amortization	896	889	2,658	2,619
Taxes other than income taxes	312	304	969	932
Estimated loss on Plant Vogtle Units 3 and 4	264	0	772	149
(Gain) loss on dispositions, net	(125)	0	(179)	(39)
Total operating expenses	4,515	3,785	13,317	11,102
Operating Income	1,723	1,835	4,029	4,156
Other Income and (Expense):
Allowance for equity funds used during construction	49	38	140	106
Earnings from equity method investments	30	33	35	105
Interest expense, net of amounts capitalized	(451)	(443)	(1,352)	(1,343)
Impairment of leveraged leases	0	0	(7)	(154)
Other income (expense), net	131	113	297	319
Total other income and (expense)	(241)	(259)	(887)	(967)
Earnings Before Income Taxes	1,482	1,576	3,142	3,189
Income taxes (benefit)	372	293	550	443
Consolidated Net Income	1,110	1,283	2,592	2,746
Dividends on preferred stock of subsidiaries	4	4	11	11
Net income (loss) attributable to noncontrolling interests	5	28	(27)	3
Net Income	$ 1,101	$ 1,251	$ 2,608	$ 2,732
Earnings per share -
Basic (in dollars per share)	$ 1.04	$ 1.18	$ 2.46	$ 2.58
Diluted (in dollars per share)	$ 1.03	$ 1.18	$ 2.44	$ 2.57
Average number of shares of common stock outstanding (in millions)
Basic (in shares)	1,061	1,058	1,060	1,058
Diluted (in shares)	1,068	1,064	1,067	1,064
Retail electric revenues
Operating Revenues:
Operating revenues	$ 4,551	$ 4,243	$ 11,492	$ 10,503
Wholesale electric revenues
Operating Revenues:
Operating revenues	731	584	1,822	1,473
Other electric revenues
Operating Revenues:
Operating revenues	179	164	525	484
Natural gas
Operating Revenues:
Operating revenues	623	477	2,994	2,362
Operating Expenses:
Total cost of sales	129	71	943	654
Other
Operating Revenues:
Operating revenues	154	152	513	436
Operating Expenses:
Total cost of sales	71	72	255	201
Fuel
Operating Expenses:
Total cost of sales	1,234	933	2,930	2,190
Purchased power
Operating Expenses:
Total cost of sales	288	230	712	611
Alternative revenue programs
Operating Revenues:
Operating revenues	(1)	(1)	3	6
ALABAMA POWER CO
Operating Revenues:
Operating revenues	1,904	1,729	5,019	4,445
Operating Expenses:
Other operations and maintenance	401	387	1,175	1,078
Depreciation and amortization	214	205	640	606
Taxes other than income taxes	99	103	303	311
Total operating expenses	1,208	1,109	3,332	2,962
Operating Income	696	620	1,687	1,483
Other Income and (Expense):
Allowance for equity funds used during construction	14	12	38	34
Interest expense, net of amounts capitalized	(84)	(84)	(252)	(255)
Other income (expense), net	29	30	93	78
Total other income and (expense)	(41)	(42)	(121)	(143)
Earnings Before Income Taxes	655	578	1,566	1,340
Income taxes (benefit)	152	130	366	307
Consolidated Net Income	503	448	1,200	1,033
Dividends on preferred stock of subsidiaries	4	4	11	11
Net Income	499	444	1,189	1,022
ALABAMA POWER CO \| Retail electric revenues
Operating Revenues:
Operating revenues	1,651	1,575	4,357	4,003
ALABAMA POWER CO \| Wholesale electric revenues
Operating Revenues:
Operating revenues	107	73	285	184
ALABAMA POWER CO \| Wholesale revenues, affiliates
Operating Revenues:
Operating revenues	53	11	109	36
ALABAMA POWER CO \| Other
Operating Revenues:
Operating revenues	93	70	268	222
ALABAMA POWER CO \| Fuel
Operating Expenses:
Total cost of sales	373	306	927	721
ALABAMA POWER CO \| Purchased power
Operating Expenses:
Total cost of sales	76	64	173	153
ALABAMA POWER CO \| Purchased power, affiliates
Operating Expenses:
Total cost of sales	45	44	114	93
GEORGIA POWER CO
Operating Revenues:
Operating revenues	2,856	2,617	7,050	6,371
Operating Expenses:
Other operations and maintenance	544	483	1,558	1,411
Depreciation and amortization	345	358	1,025	1,064
Taxes other than income taxes	130	123	365	344
Estimated loss on Plant Vogtle Units 3 and 4	264	0	772	149
Total operating expenses	2,176	1,620	5,842	4,596
Operating Income	680	997	1,208	1,775
Other Income and (Expense):
Allowance for equity funds used during construction	33	22	94	63
Interest expense, net of amounts capitalized	(106)	(106)	(315)	(322)
Other income (expense), net	42	32	124	93
Total other income and (expense)	(31)	(52)	(97)	(166)
Earnings Before Income Taxes	649	945	1,111	1,609
Income taxes (benefit)	113	172	81	198
Consolidated Net Income	536	773	1,030	1,411
GEORGIA POWER CO \| Retail electric revenues
Operating Revenues:
Operating revenues	2,652	2,435	6,465	5,870
GEORGIA POWER CO \| Wholesale electric revenues
Operating Revenues:
Operating revenues	63	34	143	85
GEORGIA POWER CO \| Other
Operating Revenues:
Operating revenues	141	148	442	416
GEORGIA POWER CO \| Fuel
Operating Expenses:
Total cost of sales	432	368	1,088	826
GEORGIA POWER CO \| Purchased power
Operating Expenses:
Total cost of sales	173	146	461	409
GEORGIA POWER CO \| Purchased power, affiliates
Operating Expenses:
Total cost of sales	288	142	573	393
MISSISSIPPI POWER CO
Operating Revenues:
Operating revenues	378	336	988	895
Operating Expenses:
Other operations and maintenance	85	62	230	202
Depreciation and amortization	46	47	138	135
Taxes other than income taxes	33	31	96	90
Total operating expenses	309	249	815	711
Operating Income	69	87	173	184
Other Income and (Expense):
Interest expense, net of amounts capitalized	(16)	(14)	(45)	(45)
Other income (expense), net	7	6	27	19
Total other income and (expense)	(9)	(8)	(18)	(26)
Earnings Before Income Taxes	60	79	155	158
Income taxes (benefit)	10	12	22	20
Consolidated Net Income	50	67	133	138
MISSISSIPPI POWER CO \| Retail electric revenues
Operating Revenues:
Operating revenues	248	232	670	630
MISSISSIPPI POWER CO \| Wholesale electric revenues
Operating Revenues:
Operating revenues	60	61	178	164
MISSISSIPPI POWER CO \| Wholesale revenues, affiliates
Operating Revenues:
Operating revenues	62	36	120	82
MISSISSIPPI POWER CO \| Other
Operating Revenues:
Operating revenues	8	7	20	19
MISSISSIPPI POWER CO \| Fuel
Operating Expenses:
Total cost of sales	139	103	330	266
MISSISSIPPI POWER CO \| Purchased power
Operating Expenses:
Total cost of sales	6	6	21	18
SOUTHERN POWER CO
Operating Revenues:
Operating revenues	679	523	1,610	1,337
Operating Expenses:
Other operations and maintenance	94	89	308	245
Depreciation and amortization	132	129	383	367
Taxes other than income taxes	12	10	35	29
Loss on sales-type lease	15	0	15	0
(Gain) loss on dispositions, net	0	0	(39)	(39)
Total operating expenses	553	384	1,328	1,000
Operating Income	126	139	282	337
Other Income and (Expense):
Interest expense, net of amounts capitalized	(36)	(36)	(111)	(114)
Other income (expense), net	2	13	10	19
Total other income and (expense)	(34)	(23)	(101)	(95)
Earnings Before Income Taxes	92	116	181	242
Income taxes (benefit)	9	14	(3)	27
Consolidated Net Income	83	102	184	215
Net income (loss) attributable to noncontrolling interests	5	28	(27)	3
Net Income	78	74	211	212
SOUTHERN POWER CO \| Wholesale electric revenues
Operating Revenues:
Operating revenues	503	418	1,231	1,047
SOUTHERN POWER CO \| Wholesale revenues, affiliates
Operating Revenues:
Operating revenues	167	101	361	279
SOUTHERN POWER CO \| Other
Operating Revenues:
Operating revenues	9	4	18	11
SOUTHERN POWER CO \| Fuel
Operating Expenses:
Total cost of sales	259	137	540	346
SOUTHERN POWER CO \| Purchased power
Operating Expenses:
Total cost of sales	41	19	86	52
SOUTHERN Co GAS
Operating Revenues:
Operating revenues	$ 623	$ 477	$ 2,994	$ 2,362
Operating Expenses:
Cost, Product and Service [Extensible Enumeration]	Natural gas	Natural gas	Natural gas	Natural gas
Other operations and maintenance	$ 238	$ 217	$ 776	$ 694
Depreciation and amortization	133	125	396	368
Taxes other than income taxes	36	35	166	154
(Gain) loss on dispositions, net	(121)	0	(127)	2
Total operating expenses	415	448	2,154	1,872
Operating Income	208	29	840	490
Other Income and (Expense):
Earnings from equity method investments	25	33	14	106
Interest expense, net of amounts capitalized	(57)	(57)	(175)	(171)
Other income (expense), net	13	12	(66)	33
Total other income and (expense)	(19)	(12)	(227)	(32)
Earnings Before Income Taxes	189	17	613	458
Income taxes (benefit)	133	3	224	98
Consolidated Net Income	56	14	389	360
SOUTHERN Co GAS \| Natural gas
Operating Revenues:
Operating revenues	624	478	2,991	2,356
Operating Expenses:
Total cost of sales	129	71	943	654
SOUTHERN Co GAS \| Alternative revenue programs
Operating Revenues:
Operating revenues	$ (1)	$ (1)	$ 3	$ 6

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating revenues	$ 6,238	$ 5,620	$ 17,346	$ 15,258
Alternative revenue programs
Operating revenues	(1)	(1)	3	6
SOUTHERN Co GAS
Operating revenues	623	477	2,994	2,362
Revenue taxes collected	12	10	89	79
SOUTHERN Co GAS \| Alternative revenue programs
Operating revenues	$ (1)	$ (1)	$ 3	$ 6

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income (loss)	$ 1,110	$ 1,283	$ 2,592	$ 2,746
Qualifying hedges:
Changes in fair value, net of tax	1	49	(15)	(26)
Reclassification adjustment for amounts included in net income, net of tax	31	(32)	81	(3)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	4	3	10	6
Total other comprehensive income (loss)	36	20	76	(23)
Comprehensive Income	1,146	1,303	2,668	2,723
Dividends on preferred stock of subsidiaries	4	4	11	11
Comprehensive income (loss) attributable to noncontrolling interests	5	28	(27)	3
Comprehensive Income (Loss) Attributable to Parent	1,137	1,271	2,684	2,709
ALABAMA POWER CO
Net income (loss)	503	448	1,200	1,033
Qualifying hedges:
Changes in fair value, net of tax	4	0	3	0
Reclassification adjustment for amounts included in net income, net of tax	1	1	3	3
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	5	1	6	3
Comprehensive Income	508	449	1,206	1,036
Dividends on preferred stock of subsidiaries	4	4	11	11
GEORGIA POWER CO
Net income (loss)	536	773	1,030	1,411
Qualifying hedges:
Changes in fair value, net of tax	0	0	0	(2)
Reclassification adjustment for amounts included in net income, net of tax	2	2	5	4
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	2	2	5	2
Comprehensive Income	538	775	1,035	1,413
MISSISSIPPI POWER CO
Net income (loss)	50	67	133	138
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	0	0	1	1
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	0	0	1	1
Comprehensive Income	50	67	134	139
SOUTHERN POWER CO
Net income (loss)	83	102	184	215
Qualifying hedges:
Changes in fair value, net of tax	(21)	44	(48)	(6)
Reclassification adjustment for amounts included in net income, net of tax	27	(36)	66	(24)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	1	0	2	2
Total other comprehensive income (loss)	7	8	20	(28)
Comprehensive Income	90	110	204	187
Comprehensive income (loss) attributable to noncontrolling interests	5	28	(27)	3
Comprehensive Income (Loss) Attributable to Parent	85	82	231	184
SOUTHERN Co GAS
Net income (loss)	56	14	389	360
Qualifying hedges:
Changes in fair value, net of tax	23	4	32	(17)
Reclassification adjustment for amounts included in net income, net of tax	(2)	1	1	7
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	21	5	33	(10)
Comprehensive Income	$ 77	$ 19	$ 422	$ 350

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Qualifying hedges:
Changes in fair value, tax	$ 1	$ 17	$ (4)	$ (9)
Reclassification adjustment for amounts included in net income, tax	10	(11)	27	(1)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, tax	1	1	4	3
ALABAMA POWER CO
Qualifying hedges:
Changes in fair value, tax	1	0	1	0
Reclassification adjustment for amounts included in net income, tax	0	0	1	1
GEORGIA POWER CO
Qualifying hedges:
Changes in fair value, tax	0	0	0	(1)
Reclassification adjustment for amounts included in net income, tax	1	0	2	2
MISSISSIPPI POWER CO
Qualifying hedges:
Reclassification adjustment for amounts included in net income, tax	0	0	0	0
SOUTHERN POWER CO
Qualifying hedges:
Changes in fair value, tax	(7)	15	(16)	(2)
Reclassification adjustment for amounts included in net income, tax	9	(13)	22	(8)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, tax	0	0	1	0
SOUTHERN Co GAS
Qualifying hedges:
Changes in fair value, tax	8	1	11	(6)
Reclassification adjustment for amounts included in net income, tax	$ 0	$ 0	$ 1	$ 2

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities:
Net income	$ 2,592	$ 2,746
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	2,944	2,903
Deferred income taxes	89	(196)
Utilization of federal investment tax credits	256	319
Allowance for equity funds used during construction	(140)	(106)
Pension, postretirement, and other employee benefits	(218)	(190)
Settlement of asset retirement obligations	(341)	(315)
Stock based compensation expense	134	99
Estimated loss on Plant Vogtle Units 3 and 4	772	149
Storm damage accruals	166	171
Impairment charges	91	154
(Gain) loss on dispositions, net	(171)	(36)
Retail fuel cost under recovery – long-term	(209)	0
Other, net	(7)	(14)
Changes in certain current assets and liabilities —
-Receivables	2	125
-Materials and supplies	(91)	(141)
-Natural gas cost under recovery	(432)	0
-Other current assets	(160)	(119)
-Accounts payable	(45)	(428)
-Accrued taxes	288	289
-Accrued compensation	(93)	(183)
-Accrued interest	(110)	(52)
-Retail fuel cost over recovery	(150)	158
-Customer refunds	(58)	(226)
-Other current liabilities	(168)	7
Net cash provided from operating activities	5,081	5,220
Investing Activities:
Business acquisitions, net of cash acquired	(345)	(81)
Property additions	(5,222)	(5,365)
Nuclear decommissioning trust fund purchases	(1,301)	(714)
Nuclear decommissioning trust fund sales	1,297	708
Proceeds from dispositions	160	987
Cost of removal, net of salvage	(282)	(233)
Payments pursuant to LTSAs	(145)	(139)
Other investing activities	(12)	(55)
Net cash used for investing activities	(5,850)	(4,892)
Financing Activities:
Decrease in notes payable	(203)	(1,534)
Proceeds —
Long-term debt	6,793	7,543
Common stock	62	63
Short-term borrowings	325	615
Redemptions and repurchases —
Long-term debt	(3,060)	(2,472)
Short-term borrowings	(25)	(840)
Capital contributions from noncontrolling interests	415	173
Distributions to noncontrolling interests	(204)	(164)
Payment of common stock dividends	(2,077)	(2,008)
Other financing activities	(224)	(299)
Net cash provided from financing activities	1,802	1,077
Net Change in Cash, Cash Equivalents, and Restricted Cash	1,033	1,405
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	1,068	1,978
Cash, Cash Equivalents, and Restricted Cash at End of Period	2,101	3,383
Cash paid during the period for —
Interest, net of amounts capitalized	1,417	1,346
Income taxes, net	92	66
Noncash transactions —
Accrued property additions at end of period	915	917
Contributions from noncontrolling interests	89	9
Contributions of wind turbine equipment	82	17
Right-of-use assets obtained under finance leases	92	166
ALABAMA POWER CO
Operating Activities:
Net income	1,200	1,033
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	748	731
Deferred income taxes	104	71
Allowance for equity funds used during construction	(38)	(34)
Pension, postretirement, and other employee benefits	(74)	(71)
Settlement of asset retirement obligations	(152)	(157)
Other, net	(51)	33
Changes in certain current assets and liabilities —
-Receivables	(128)	(130)
-Fossil fuel stock	91	4
-Prepayments	(24)	(32)
-Materials and supplies	(13)	(55)
-Retail fuel cost under recovery	(79)	0
-Other current assets	(19)	(35)
-Accounts payable	(230)	(248)
-Accrued taxes	178	142
-Accrued compensation	(37)	(55)
-Retail fuel cost over recovery	(18)	74
-Other current liabilities	(77)	(76)
Net cash provided from operating activities	1,419	1,229
Investing Activities:
Property additions	(1,235)	(1,460)
Nuclear decommissioning trust fund purchases	(536)	(213)
Nuclear decommissioning trust fund sales	536	213
Cost of removal, net of salvage	(93)	(68)
Change in construction payables, net	12	(46)
Other investing activities	(19)	(17)
Net cash used for investing activities	(1,335)	(1,591)
Proceeds —
Senior notes	600	600
Pollution control revenue bonds	0	87
Redemptions and repurchases —
Pollution control revenue bonds	0	(87)
Other long-term debt	(206)	0
Senior notes	(200)	0
Capital contributions from parent company	630	649
Payment of common stock dividends	(738)	(718)
Other financing activities	(30)	(26)
Net cash provided from financing activities	56	505
Net Change in Cash, Cash Equivalents, and Restricted Cash	140	143
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	530	894
Cash, Cash Equivalents, and Restricted Cash at End of Period	670	1,037
Cash paid during the period for —
Interest, net of amounts capitalized	246	249
Income taxes, net	183	203
Noncash transactions —
Accrued property additions at end of period	178	154
Right-of-use assets obtained under leases	2	65
GEORGIA POWER CO
Operating Activities:
Net income	1,030	1,411
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	1,164	1,206
Deferred income taxes	(299)	(167)
Allowance for equity funds used during construction	(94)	(63)
Pension, postretirement, and other employee benefits	(112)	(98)
Settlement of asset retirement obligations	(154)	(130)
Estimated loss on Plant Vogtle Units 3 and 4	772	149
Storm damage accruals	160	160
Retail fuel cost under recovery – long-term	(203)	0
Other, net	88	11
Changes in certain current assets and liabilities —
-Receivables	(85)	(168)
-Fossil fuel stock	77	4
-Materials and supplies	(60)	(74)
-Other current assets	(51)	(69)
-Accounts payable	164	25
-Accrued taxes	154	44
-Retail fuel cost over recovery	(113)	84
-Customer refunds	(5)	(162)
-Other current liabilities	(83)	(38)
Net cash provided from operating activities	2,350	2,125
Investing Activities:
Property additions	(2,411)	(2,519)
Nuclear decommissioning trust fund purchases	(766)	(500)
Nuclear decommissioning trust fund sales	761	495
Proceeds from dispositions	4	143
Cost of removal, net of salvage	(99)	(93)
Change in construction payables, net	(68)	(14)
Payments pursuant to LTSAs	(38)	(44)
Contributions in aid of construction	71	18
Other investing activities	(26)	(12)
Net cash used for investing activities	(2,572)	(2,526)
Financing Activities:
Decrease in notes payable	(60)	(115)
Proceeds —
Senior notes	750	1,500
Pollution control revenue bonds	122	53
FFB loan	371	519
Short-term borrowings	0	250
Redemptions and repurchases —
Short-term borrowings	0	(375)
Pollution control revenue bonds	(69)	(148)
Senior notes	(325)	(950)
FFB loan	(75)	(55)
Capital contributions from parent company	1,054	1,379
Payment of common stock dividends	(1,237)	(1,156)
Other financing activities	(26)	(35)
Net cash provided from financing activities	505	867
Net Change in Cash, Cash Equivalents, and Restricted Cash	283	466
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	9	52
Cash, Cash Equivalents, and Restricted Cash at End of Period	292	518
Cash paid during the period for —
Interest, net of amounts capitalized	325	316
Income taxes, net	237	311
Noncash transactions —
Accrued property additions at end of period	477	523
Right-of-use assets obtained under operating leases	3	30
MISSISSIPPI POWER CO
Operating Activities:
Net income	133	138
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	161	142
Settlement of asset retirement obligations	(18)	(16)
Other, net	(20)	(11)
Changes in certain current assets and liabilities —
-Receivables	(19)	(3)
-Other current assets	(9)	(7)
-Accounts payable	(12)	(54)
-Accrued taxes	(20)	15
-Retail fuel cost over recovery	(19)	0
-Other current liabilities	(18)	(18)
Net cash provided from operating activities	159	186
Investing Activities:
Property additions	(135)	(174)
Change in construction payables, net	(11)	7
Payments pursuant to LTSAs	(21)	(20)
Other investing activities	(15)	(13)
Net cash used for investing activities	(182)	(200)
Financing Activities:
Decrease in notes payable	(25)	0
Proceeds —
Senior notes	525	0
Pollution control revenue bonds	0	34
Short-term borrowings	0	40
Other long-term debt	0	100
Redemptions and repurchases —
Short-term borrowings	0	(40)
Pollution control revenue bonds	0	(41)
Other revenue bonds	(270)	0
Other long-term debt	(75)	0
Senior notes	0	(275)
Capital contributions from parent company	103	80
Return of capital to parent company	0	(74)
Payment of common stock dividends	(118)	(37)
Other financing activities	(10)	(1)
Net cash provided from financing activities	130	(214)
Net Change in Cash, Cash Equivalents, and Restricted Cash	107	(228)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	39	286
Cash, Cash Equivalents, and Restricted Cash at End of Period	146	58
Cash paid during the period for —
Interest, net of amounts capitalized	53	49
Income taxes, net	11	9
Noncash transactions —
Accrued property additions at end of period	23	42
SOUTHERN POWER CO
Operating Activities:
Net income	184	215
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	402	386
Deferred income taxes	(16)	(59)
Utilization of federal investment tax credits	237	318
Amortization of investment tax credits	(44)	(44)
(Gain) loss on dispositions, net	(39)	(39)
Other, net	14	(16)
Changes in certain current assets and liabilities —
-Receivables	(117)	(28)
-Prepaid income taxes	63	74
-Other current assets	(5)	(17)
-Accounts payable	55	(12)
-Accrued taxes	15	21
-Other current liabilities	1	(25)
Net cash provided from operating activities	750	774
Investing Activities:
Business acquisitions, net of cash acquired	(345)	(81)
Property additions	(355)	(135)
Proceeds from dispositions	22	663
Change in construction payables, net	(22)	(12)
Payments pursuant to LTSAs	(61)	(61)
Other investing activities	8	50
Net cash used for investing activities	(753)	424
Financing Activities:
Decrease in notes payable	(148)	(449)
Proceeds —
Senior notes	400	0
Redemptions and repurchases —
Short-term borrowings	0	(100)
Senior notes	0	(300)
Return of capital to parent company	(271)	0
Capital contributions from noncontrolling interests	415	173
Distributions to noncontrolling interests	(204)	(164)
Purchase of membership interests from noncontrolling interests	0	(60)
Payment of common stock dividends	(153)	(151)
Other financing activities	(6)	(9)
Net cash provided from financing activities	33	(1,060)
Net Change in Cash, Cash Equivalents, and Restricted Cash	30	138
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	183	279
Cash, Cash Equivalents, and Restricted Cash at End of Period	213	417
Cash paid during the period for —
Interest, net of amounts capitalized	118	123
Income taxes, net	(235)	(278)
Noncash transactions —
Accrued property additions at end of period	53	44
Contributions from noncontrolling interests	89	9
Contributions of wind turbine equipment	82	17
Right-of-use assets obtained under operating leases	66	30
SOUTHERN Co GAS
Operating Activities:
Net income	389	360
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	396	368
Deferred income taxes	289	(1)
Mark-to-market adjustments	147	104
Impairment of PennEast Pipeline investment	84	0
(Gain) loss on dispositions, net	(127)	2
Natural gas cost under recovery – long-term	(79)	0
Other, net	32	(21)
Changes in certain current assets and liabilities —
-Receivables	311	403
-Prepaid income taxes	(148)	(19)
-Natural gas cost under recovery	(432)	0
-Other current assets	(78)	(1)
-Accounts payable	30	(75)
-Other current liabilities	(57)	2
Net cash provided from operating activities	757	1,122
Investing Activities:
Property additions	(1,045)	(1,045)
Proceeds from dispositions	126	178
Cost of removal, net of salvage	(74)	(60)
Investment in unconsolidated subsidiaries	(3)	(79)
Other investing activities	30	33
Net cash used for investing activities	(966)	(973)
Financing Activities:
Increase in notes payable	38
Decrease in notes payable		(500)
Proceeds —
Senior notes	450	500
Short-term borrowings	300	0
First mortgage bonds	100	150
Redemptions and repurchases —
Senior notes	(300)	0
Medium-term notes	(30)	0
Capital contributions from parent company	63	215
Payment of common stock dividends	(397)	(399)
Other financing activities	(2)	(3)
Net cash provided from financing activities	222	(37)
Net Change in Cash, Cash Equivalents, and Restricted Cash	13	112
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	19	49
Cash, Cash Equivalents, and Restricted Cash at End of Period	32	161
Cash paid during the period for —
Interest, net of amounts capitalized	173	162
Income taxes, net	85	45
Noncash transactions —
Accrued property additions at end of period	$ 146	$ 146

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Interest capitalized	$ 68	$ 61
ALABAMA POWER CO
Interest capitalized	11	11
GEORGIA POWER CO
Interest capitalized	47	34
SOUTHERN POWER CO
Interest capitalized	5	10
SOUTHERN Co GAS
Interest capitalized	$ 6	$ 5

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 2,078	$ 1,065
Receivables —
Customer accounts	1,831	1,753
Energy marketing	0	516
Unbilled revenues	535	672
Other accounts and notes	611	512
Accumulated provision for uncollectible accounts	(72)	(118)
Materials and supplies	1,504	1,478
Fossil fuel for generation	386	550
Natural gas for sale	368	460
Prepaid expenses	329	276
Assets from risk management activities, net of collateral	365	147
Regulatory assets – asset retirement obligations	233	214
Natural gas cost under recovery	432	0
Other regulatory assets	792	810
Other current assets	282	282
Total current assets	9,674	8,617
Property, Plant, and Equipment:
In service	114,166	110,516
Less: Accumulated depreciation	33,723	32,397
Plant in service, net of depreciation	80,443	78,119
Nuclear fuel, at amortized cost	805	818
Construction work in progress	9,611	8,697
Total property, plant, and equipment	90,859	87,634
Other Property and Investments:
Goodwill	5,280	5,280
Nuclear decommissioning trusts, at fair value	2,446	2,303
Equity investments in unconsolidated subsidiaries	1,278	1,362
Other intangible assets, net of amortization	455	487
Leveraged leases	575	556
Miscellaneous property and investments	586	398
Total other property and investments	10,620	10,386
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,724	1,802
Deferred charges related to income taxes	815	796
Unamortized loss on reacquired debt	263	280
Regulatory assets – asset retirement obligations, deferred	5,418	4,934
Other regulatory assets, deferred	6,902	7,198
Other deferred charges and assets	1,586	1,288
Total deferred charges and other assets	16,708	16,298
Total Assets	127,861	122,935
Current Liabilities:
Securities due within one year	3,286	3,507
Notes payable	707	609
Energy marketing trade payables	0	494
Accounts payable —
Accounts payable	2,229	2,312
Customer deposits	493	487
Accrued taxes —
Accrued income taxes	149	130
Other accrued taxes	797	699
Accrued interest	404	513
Accrued compensation	908	1,025
Asset retirement obligations	690	585
Operating lease obligations	246	241
Other regulatory liabilities	555	509
Other current liabilities	795	968
Total current liabilities	11,259	12,079
Long-term Debt	48,843	45,073
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	8,916	8,175
Deferred credits related to income taxes	5,485	5,767
Accumulated deferred ITCs	2,230	2,235
Employee benefit obligations	1,849	2,213
Operating lease obligations, deferred	1,495	1,611
Asset retirement obligations, deferred	10,919	10,099
Accrued environmental remediation	203	216
Other cost of removal obligations	2,164	2,211
Other regulatory liabilities, deferred	351	251
Other deferred credits and liabilities	637	480
Total deferred credits and other liabilities	34,249	33,258
Total Liabilities	94,351	90,410
Redeemable Preferred Stock of Subsidiaries	291	291
Common Stockholder's Equity (See accompanying statements)	33,219	32,234
Total Liabilities and Stockholders' Equity	127,861	122,935
ALABAMA POWER CO
Current Assets:
Cash and cash equivalents	670	530
Receivables —
Customer accounts	497	429
Unbilled revenues	151	152
Affiliated	53	31
Other accounts and notes	101	66
Accumulated provision for uncollectible accounts	(18)	(43)
Materials and supplies	556	546
Fossil fuel for generation	144	235
Prepaid expenses	65	42
Other regulatory assets	289	226
Other current assets	107	33
Total current assets	2,615	2,247
Property, Plant, and Equipment:
In service	32,787	31,816
Less: Accumulated depreciation	10,298	10,009
Plant in service, net of depreciation	22,489	21,807
Nuclear fuel, at amortized cost	241	270
Construction work in progress	1,129	866
Total property, plant, and equipment	23,859	22,943
Other Property and Investments:
Nuclear decommissioning trusts, at fair value	1,259	1,157
Equity investments in unconsolidated subsidiaries	57	63
Miscellaneous property and investments	129	131
Total other property and investments	1,445	1,351
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	119	151
Deferred charges related to income taxes	238	235
Regulatory assets – asset retirement obligations, deferred	1,580	1,441
Other regulatory assets, deferred	2,100	2,162
Other deferred charges and assets	348	273
Total deferred charges and other assets	4,385	4,262
Total Assets	32,304	30,803
Current Liabilities:
Securities due within one year	616	311
Accounts payable —
Affiliated	299	316
Other	370	545
Customer deposits	106	104
Accrued taxes —
Accrued taxes	331	152
Accrued interest	79	90
Accrued compensation	191	212
Asset retirement obligations	308	254
Other regulatory liabilities	72	108
Other current liabilities	122	107
Total current liabilities	2,494	2,199
Long-term Debt	8,443	8,558
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,425	3,273
Deferred credits related to income taxes	1,973	2,016
Accumulated deferred ITCs	89	94
Employee benefit obligations	136	214
Operating lease obligations, deferred	69	119
Asset retirement obligations, deferred	4,015	3,720
Other cost of removal obligations	261	335
Other regulatory liabilities, deferred	139	124
Other deferred credits and liabilities	66	50
Total deferred credits and other liabilities	10,173	9,945
Total Liabilities	21,110	20,702
Redeemable Preferred Stock	291	291
Common Stockholder's Equity (See accompanying statements)	10,903	9,810
Total Liabilities and Stockholders' Equity	32,304	30,803
GEORGIA POWER CO
Current Assets:
Cash and cash equivalents	292	9
Receivables —
Customer accounts	689	621
Unbilled revenues	258	233
Joint owner accounts	106	123
Affiliated	41	21
Other accounts and notes	46	67
Accumulated provision for uncollectible accounts	(2)	(26)
Materials and supplies	647	592
Fossil fuel for generation	201	278
Regulatory assets – storm damage	102	213
Regulatory assets – asset retirement obligations	191	166
Other regulatory assets	243	248
Other current assets	255	143
Total current assets	3,069	2,688
Property, Plant, and Equipment:
In service	40,831	39,682
Less: Accumulated depreciation	12,743	12,251
Plant in service, net of depreciation	28,088	27,431
Nuclear fuel, at amortized cost	564	548
Construction work in progress	7,337	6,857
Total property, plant, and equipment	35,989	34,836
Other Property and Investments:
Nuclear decommissioning trusts, at fair value	1,187	1,145
Equity investments in unconsolidated subsidiaries	50	51
Miscellaneous property and investments	66	63
Total other property and investments	1,303	1,259
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,193	1,308
Deferred charges related to income taxes	544	527
Regulatory assets – asset retirement obligations, deferred	3,607	3,291
Other regulatory assets, deferred	2,515	2,692
Other deferred charges and assets	712	479
Total deferred charges and other assets	8,571	8,297
Total Assets	48,932	47,080
Current Liabilities:
Securities due within one year	672	542
Notes payable	0	60
Accounts payable —
Affiliated	719	597
Other	761	753
Customer deposits	263	276
Accrued taxes —
Accrued taxes	457	407
Accrued interest	98	130
Accrued compensation	207	233
Asset retirement obligations	333	287
Operating lease obligations	153	151
Other regulatory liabilities	360	228
Over recovered fuel clause revenues	0	113
Other current liabilities	198	254
Total current liabilities	4,221	4,031
Long-term Debt	13,064	12,428
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,222	3,272
Deferred credits related to income taxes	2,386	2,588
Accumulated deferred ITCs	321	273
Employee benefit obligations	461	586
Operating lease obligations, deferred	1,008	1,156
Asset retirement obligations, deferred	6,432	5,978
Other deferred credits and liabilities	456	267
Total deferred credits and other liabilities	14,286	14,120
Total Liabilities	31,571	30,579
Common Stockholder's Equity (See accompanying statements)	17,361	16,501
Total Liabilities and Stockholders' Equity	48,932	47,080
MISSISSIPPI POWER CO
Current Assets:
Cash and cash equivalents	146	39
Receivables —
Customer accounts	46	34
Unbilled revenues	39	38
Affiliated	45	32
Other accounts and notes	27	32
Materials and supplies	71	65
Fossil fuel for generation	27	24
Assets from risk management activities, net of collateral	66	1
Other regulatory assets	54	60
Other current assets	11	19
Total current assets	532	344
Property, Plant, and Equipment:
In service	5,078	5,011
Less: Accumulated depreciation	1,568	1,545
Plant in service, net of depreciation	3,510	3,466
Construction work in progress	117	146
Total property, plant, and equipment	3,627	3,612
Other Property and Investments:
Total other property and investments	180	151
Deferred Charges and Other Assets:
Deferred charges related to income taxes	31	32
Regulatory assets – asset retirement obligations, deferred	231	201
Other regulatory assets, deferred	371	388
Accumulated deferred income taxes	119	129
Other deferred charges and assets	100	55
Total deferred charges and other assets	852	805
Total Assets	5,191	4,912
Current Liabilities:
Securities due within one year	76	406
Notes payable	0	25
Accounts payable —
Affiliated	88	63
Other	61	109
Accrued taxes —
Accrued taxes	94	114
Accrued interest	7	15
Accrued compensation	31	34
Asset retirement obligations	19	27
Other regulatory liabilities	104	49
Over recovered fuel clause revenues	7	34
Other current liabilities	50	40
Total current liabilities	537	916
Long-term Debt	1,509	1,013
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	464	447
Deferred credits related to income taxes	276	287
Employee benefit obligations	94	113
Asset retirement obligations, deferred	175	150
Other cost of removal obligations	194	194
Other regulatory liabilities, deferred	48	15
Other deferred credits and liabilities	31	35
Total deferred credits and other liabilities	1,282	1,241
Total Liabilities	3,328	3,170
Common Stockholder's Equity (See accompanying statements)	1,863	1,742
Total Liabilities and Stockholders' Equity	5,191	4,912
SOUTHERN POWER CO
Current Assets:
Cash and cash equivalents	192	182
Receivables —
Customer accounts	178	125
Affiliated	68	37
Other accounts and notes	53	27
Materials and supplies	103	157
Prepaid income taxes	15	11
Other current assets	56	36
Total current assets	665	575
Property, Plant, and Equipment:
In service	14,399	13,904
Less: Accumulated depreciation	3,122	2,842
Plant in service, net of depreciation	11,277	11,062
Construction work in progress	274	127
Total property, plant, and equipment	11,551	11,189
Other Property and Investments:
Intangible assets, net of amortization	288	302
Equity investments in unconsolidated subsidiaries	83	19
Net investment in sales-type lease	91	0
Total other property and investments	462	321
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	475	415
Prepaid LTSAs	191	155
Accumulated deferred income taxes	0	262
Income taxes receivable, non-current	33	25
Other deferred charges and assets	234	293
Total deferred charges and other assets	933	1,150
Total Assets	13,611	13,235
Current Liabilities:
Securities due within one year	994	299
Notes payable	27	175
Accounts payable —
Affiliated	110	65
Other	91	92
Accrued taxes —
Accrued income taxes	8	8
Other accrued taxes	27	22
Accrued interest	26	32
Other current liabilities	125	132
Total current liabilities	1,408	825
Long-term Debt	3,021	3,393
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	156	123
Accumulated deferred ITCs	1,629	1,672
Operating lease obligations, deferred	489	426
Other deferred credits and liabilities	201	165
Total deferred credits and other liabilities	2,475	2,386
Total Liabilities	6,904	6,604
Common Stockholder's Equity (See accompanying statements)	6,707	6,631
Total Liabilities and Stockholders' Equity	13,611	13,235
SOUTHERN Co GAS
Current Assets:
Cash and cash equivalents	29	17
Receivables —
Customer accounts	249	353
Energy marketing	0	516
Unbilled revenues	70	219
Affiliated	1	4
Other accounts and notes	39	51
Accumulated provision for uncollectible accounts	(37)	(40)
Natural gas for sale	368	460
Prepaid expenses	181	48
Assets from risk management activities, net of collateral	75	118
Natural gas cost under recovery	432	0
Other regulatory assets	137	102
Other current assets	44	38
Total current assets	1,588	1,886
Property, Plant, and Equipment:
In service	18,527	17,611
Less: Accumulated depreciation	5,004	4,821
Plant in service, net of depreciation	13,523	12,790
Construction work in progress	691	648
Total property, plant, and equipment	14,214	13,438
Other Property and Investments:
Goodwill	5,015	5,015
Equity investments in unconsolidated subsidiaries	1,174	1,290
Other intangible assets, net of amortization	40	51
Miscellaneous property and investments	20	19
Total other property and investments	6,249	6,375
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	72	81
Other regulatory assets, deferred	634	615
Other deferred charges and assets	201	235
Total deferred charges and other assets	907	931
Total Assets	22,958	22,630
Current Liabilities:
Securities due within one year	47	333
Notes payable	662	324
Energy marketing trade payables	0	494
Accounts payable —
Affiliated	42	56
Other	399	373
Customer deposits	106	90
Accrued taxes —
Accrued taxes	79	83
Accrued interest	68	58
Accrued compensation	87	106
Other regulatory liabilities	18	122
Temporary LIFO liquidation	18	0
Other current liabilities	154	150
Total current liabilities	1,680	2,189
Long-term Debt	6,766	6,293
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,571	1,265
Deferred credits related to income taxes	822	847
Employee benefit obligations	260	283
Operating lease obligations, deferred	60	67
Accrued environmental remediation	203	216
Other cost of removal obligations	1,675	1,649
Other deferred credits and liabilities	45	54
Total deferred credits and other liabilities	4,636	4,381
Total Liabilities	13,082	12,863
Common Stockholder's Equity (See accompanying statements)	9,876	9,767
Total Liabilities and Stockholders' Equity	$ 22,958	$ 22,630

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Other intangible assets, amortization	$ 296	$ 328
SOUTHERN POWER CO
Other intangible assets, amortization	104	89
SOUTHERN Co GAS
Other intangible assets, amortization	$ 142	$ 195

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	ALABAMA POWER CO	ALABAMA POWER COCommon Stock	ALABAMA POWER COPaid-In Capital	ALABAMA POWER CORetained Earnings (Accumulated Deficit)	ALABAMA POWER COAccumulated Other Comprehensive Income (Loss)	GEORGIA POWER CO	GEORGIA POWER COCommon Stock	GEORGIA POWER COPaid-In Capital	GEORGIA POWER CORetained Earnings (Accumulated Deficit)	GEORGIA POWER COAccumulated Other Comprehensive Income (Loss)	MISSISSIPPI POWER CO	MISSISSIPPI POWER COCommon Stock	MISSISSIPPI POWER COPaid-In Capital	MISSISSIPPI POWER CORetained Earnings (Accumulated Deficit)	MISSISSIPPI POWER COAccumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CO	SOUTHERN POWER COTotal Common Stockholders' Equity	SOUTHERN POWER COPaid-In Capital	SOUTHERN POWER CORetained Earnings (Accumulated Deficit)	SOUTHERN POWER COAccumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CONoncontrolling Interests	SOUTHERN Co GAS	SOUTHERN Co GASPaid-In Capital	SOUTHERN Co GASRetained Earnings (Accumulated Deficit)	SOUTHERN Co GASAccumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2019		1,054	1						31					9					1
Beginning balance at Dec. 31, 2019	$ 31,759	$ 5,257	$ (42)	$ 11,734	$ 10,877	$ (321)	$ 4,254	$ 8,955	$ 1,222	$ 4,755	$ 3,001	$ (23)	$ 15,065	$ 398	$ 10,962	$ 3,756	$ (51)	$ 1,652	$ 38	$ 4,449	$ (2,832)	$ (3)	$ 6,622	$ 2,368	$ 909	$ 1,485	$ (26)	$ 4,254	$ 9,506	$ 9,697	$ (198)	$ 7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	837				868		(31)
Net income (loss)													331			331		32			32		44	75		75		(31)	275		275
Net income after dividends on preferred stock								280			280
Capital contributions from parent company								612		612			502		502			76		76
Return of capital to parent company																		(37)		(37)									(2)	(2)
Other comprehensive income (loss)	(47)					(47)		1				1	(1)				(1)						(33)	(33)			(33)		(15)			(15)
Stock issued (in shares)		3
Stock issued	52	$ 9		43
Stock-based compensation	5			5
Cash dividends on common stock	(655)				(655)			(239)			(239)		(385)			(385)							(50)	(50)		(50)			(133)		(133)
Capital contributions from noncontrolling interests	16						16																16					16
Distributions to noncontrolling interests	(48)						(48)																(48)					(48)
Other	(3)		$ (2)		(2)	1												(1)		(1)
Ending balance (in shares) at Mar. 31, 2020		1,057	1						31					9					1
Ending balance at Mar. 31, 2020	31,916	$ 5,266	$ (44)	11,782	11,088	(367)	4,191	9,609	$ 1,222	5,367	3,042	(22)	15,512	$ 398	11,464	3,702	(52)	1,722	$ 38	4,487	(2,800)	(3)	6,551	2,360	909	1,510	(59)	4,191	9,631	9,695	(56)	(8)
Beginning balance (in shares) at Dec. 31, 2019		1,054	1						31					9					1
Beginning balance at Dec. 31, 2019	31,759	$ 5,257	$ (42)	11,734	10,877	(321)	4,254	8,955	$ 1,222	4,755	3,001	(23)	15,065	$ 398	10,962	3,756	(51)	1,652	$ 38	4,449	(2,832)	(3)	6,622	2,368	909	1,485	(26)	4,254	9,506	9,697	(198)	7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,746							1,033					1,411					138					215						360
Net income after dividends on preferred stock	2,732																												360
Purchase of membership interests from noncontrolling interests																							60
Ending balance (in shares) at Sep. 30, 2020		1,057	1						31					9					1
Ending balance at Sep. 30, 2020	32,500	$ 5,267	$ (44)	11,810	11,600	(344)	4,211	9,915	$ 1,222	5,408	3,305	(20)	16,706	$ 398	12,345	4,011	(48)	1,760	$ 38	4,456	(2,731)	(3)	6,611	2,400	908	1,546	(54)	4,211	9,685	9,925	(237)	(3)
Beginning balance (in shares) at Mar. 31, 2020		1,057	1						31					9					1
Beginning balance at Mar. 31, 2020	31,916	$ 5,266	$ (44)	11,782	11,088	(367)	4,191	9,609	$ 1,222	5,367	3,042	(22)	15,512	$ 398	11,464	3,702	(52)	1,722	$ 38	4,487	(2,800)	(3)	6,551	2,360	909	1,510	(59)	4,191	9,631	9,695	(56)	(8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	617				612		5
Net income (loss)													308			308		39			39		68	63		63		5	71		71
Net income after dividends on preferred stock								298			298
Capital contributions from parent company								1		1			1		1														200	200
Return of capital to parent company																		(37)		(37)
Other comprehensive income (loss)	4					4		1				1	2				2						(3)	(3)			(3)
Stock issued	7			7
Stock-based compensation	11			11
Cash dividends on common stock	(677)				(677)			(239)			(239)		(386)			(386)							(50)	(50)		(50)			(133)		(133)
Capital contributions from noncontrolling interests	165						165																165					165
Distributions to noncontrolling interests	(70)						(70)																(70)					(70)
Other	(12)			(13)	1																		(2)	(2)	(2)
Ending balance (in shares) at Jun. 30, 2020		1,057	1						31					9					1
Ending balance at Jun. 30, 2020	31,961	$ 5,266	$ (44)	11,787	11,024	(363)	4,291	9,670	$ 1,222	5,368	3,101	(21)	15,437	$ 398	11,465	3,624	(50)	1,724	$ 38	4,450	(2,761)	(3)	6,659	2,368	907	1,523	(62)	4,291	9,769	9,895	(118)	(8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	1,279				1,251		28
Net income (loss)	1,283							448					773			773		67			67		102	74		74		28	14		14
Net income after dividends on preferred stock	1,251							444			444																		14
Capital contributions from parent company								40		40			880		880			6		6									30	30
Return of capital to parent company																							(4)	(4)	(4)
Other comprehensive income (loss)	20					20		1				1	2				2						8	8			8		5			5
Stock issued (in shares)		0
Stock issued	4	$ 1		3
Stock-based compensation	15			15
Cash dividends on common stock	(676)				(676)			(240)			(240)		(386)			(386)		(37)			(37)		(51)	(51)		(51)			(133)		(133)
Capital contributions from noncontrolling interests	2						2																2					2
Distributions to noncontrolling interests	(51)						(51)																(51)					(51)
Purchase of membership interests from noncontrolling interests																								5	5
Purchase of membership interests from noncontrolling interests	(55)						(60)																(55)					(60)
Other	1		$ 0	0	1	(1)	1
Ending balance (in shares) at Sep. 30, 2020		1,057	1						31					9					1
Ending balance at Sep. 30, 2020	32,500	$ 5,267	$ (44)	11,810	11,600	(344)	4,211	9,915	$ 1,222	5,408	3,305	(20)	16,706	$ 398	12,345	4,011	(48)	1,760	$ 38	4,456	(2,731)	(3)	6,611	2,400	908	1,546	(54)	4,211	9,685	9,925	(237)	(3)
Beginning balance (in shares) at Dec. 31, 2020		1,058	1						31					9					1
Beginning balance at Dec. 31, 2020	32,234	$ 5,268	$ (46)	11,834	11,311	(395)	4,262	9,810	$ 1,222	5,413	3,194	(19)	16,501	$ 398	12,361	3,789	(47)	1,742	$ 38	4,460	(2,754)	(2)	6,631	2,369	914	1,522	(67)	4,262	9,767	9,930	(141)	(22)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	1,103				1,135		(32)
Net income (loss)													351			351		45			45		65	97		97		(32)	398		398
Net income after dividends on preferred stock								359			359
Capital contributions from parent company								602		602			332		332			100		100									57	57
Return of capital to parent company																							(271)	(271)	(271)
Other comprehensive income (loss)	28					28		1				1	2				2						16	16			16		4			4
Stock issued (in shares)		2
Stock issued	14	$ 5		9
Stock-based compensation	9			9
Cash dividends on common stock	(678)				(678)			(246)			(246)		(412)			(412)		(39)			(39)		(51)	(51)		(51)			(132)		(132)
Capital contributions from noncontrolling interests	403						403																403					403
Distributions to noncontrolling interests	(46)						(46)																(46)					(46)
Other	1			2			(1)																(3)	(2)	(2)	1	(1)	(1)
Ending balance (in shares) at Mar. 31, 2021		1,060	1						31					9					1
Ending balance at Mar. 31, 2021	33,068	$ 5,273	$ (46)	11,854	11,768	(367)	4,586	10,526	$ 1,222	6,015	3,307	(18)	16,774	$ 398	12,693	3,728	(45)	1,848	$ 38	4,560	(2,748)	(2)	6,744	2,158	641	1,569	(52)	4,586	10,094	9,987	125	(18)
Beginning balance (in shares) at Dec. 31, 2020		1,058	1						31					9					1
Beginning balance at Dec. 31, 2020	32,234	$ 5,268	$ (46)	11,834	11,311	(395)	4,262	9,810	$ 1,222	5,413	3,194	(19)	16,501	$ 398	12,361	3,789	(47)	1,742	$ 38	4,460	(2,754)	(2)	6,631	2,369	914	1,522	(67)	4,262	9,767	9,930	(141)	(22)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,592							1,200					1,030					133					184						389
Net income after dividends on preferred stock	2,608																												389
Purchase of membership interests from noncontrolling interests																							0
Ending balance (in shares) at Sep. 30, 2021		1,061	1						31					9					1
Ending balance at Sep. 30, 2021	33,219	$ 5,278	$ (46)	11,932	11,844	(319)	4,530	10,903	$ 1,222	6,050	3,644	(13)	17,361	$ 398	13,423	3,582	(42)	1,863	$ 38	4,565	(2,739)	(1)	6,707	2,177	643	1,581	(47)	4,530	9,876	10,014	(149)	11
Beginning balance (in shares) at Mar. 31, 2021		1,060	1						31					9					1
Beginning balance at Mar. 31, 2021	33,068	$ 5,273	$ (46)	11,854	11,768	(367)	4,586	10,526	$ 1,222	6,015	3,307	(18)	16,774	$ 398	12,693	3,728	(45)	1,848	$ 38	4,560	(2,748)	(2)	6,744	2,158	641	1,569	(52)	4,586	10,094	9,987	125	(18)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	372				372
Net income (loss)													143			143		38			38		36	36		36			(65)		(65)
Net income after dividends on preferred stock								331			331
Capital contributions from parent company								26		26			40		40			2		2									25	25
Other comprehensive income (loss)	12					12		1				1	1				1						(3)	(3)			(3)		8			8
Stock issued	10	$ 1		9
Stock-based compensation	22			22
Cash dividends on common stock	(699)				(699)			(246)			(246)		(412)			(412)		(39)			(39)		(51)	(51)		(51)			(133)		(133)
Capital contributions from noncontrolling interests	29						29																29					29
Distributions to noncontrolling interests	(68)						(68)																(68)					(68)
Other	0		$ (2)	1	1			(1)			(1)							0			(1)	1	3	3	2		1
Ending balance (in shares) at Jun. 30, 2021		1,060	1						31					9					1
Ending balance at Jun. 30, 2021	32,746	$ 5,274	$ (48)	11,886	11,442	(355)	4,547	10,637	$ 1,222	6,041	3,391	(17)	16,546	$ 398	12,733	3,459	(44)	1,849	$ 38	4,562	(2,750)	(1)	6,690	2,143	643	1,554	(54)	4,547	9,929	10,012	(73)	(10)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	1,106				1,101		5
Net income (loss)	1,110							503					536			536		50			50		83	78		78		5	56		56
Net income after dividends on preferred stock	1,101							499			499																		56
Capital contributions from parent company								9		9			690		690			3		3									2	2
Other comprehensive income (loss)	36					36		5				5	2				2						7	7			7		21			21
Stock issued (in shares)		1
Stock issued	38	$ 4		34
Stock-based compensation	22			22
Cash dividends on common stock	(700)				(700)			(246)			(246)		(413)			(413)		(39)			(39)		(51)	(51)		(51)			(132)		(132)
Capital contributions from noncontrolling interests	72						72																73					73
Distributions to noncontrolling interests	(94)						(94)																(95)					(95)
Other	(7)		$ 2	(10)	1	0	0	(1)	$ 0	0	0	(1)											1					1
Ending balance (in shares) at Sep. 30, 2021		1,061	1						31					9					1
Ending balance at Sep. 30, 2021	$ 33,219	$ 5,278	$ (46)	$ 11,932	$ 11,844	$ (319)	$ 4,530	$ 10,903	$ 1,222	$ 6,050	$ 3,644	$ (13)	$ 17,361	$ 398	$ 13,423	$ 3,582	$ (42)	$ 1,863	$ 38	$ 4,565	$ (2,739)	$ (1)	$ 6,707	$ 2,177	$ 643	$ 1,581	$ (47)	$ 4,530	$ 9,876	$ 10,014	$ (149)	$ 11

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Statement of Stockholders' Equity [Abstract]
Cash dividends (in dollars per share)	$ 0.66	$ 0.66	$ 0.64	$ 0.64	$ 0.64	$ 0.62

Introduction

Introduction	9 Months Ended
Introduction	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Introduction	INTRODUCTION The condensed quarterly financial statements of each Registrant included herein have been prepared by such Registrant, without audit, pursuant to the rules and regulations of the SEC. The Condensed Balance Sheets at December 31, 2020 have been derived from the audited financial statements of each Registrant. In the opinion of each Registrant's management, the information regarding such Registrant furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended September 30, 2021 and 2020. Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although each Registrant believes that the disclosures regarding such Registrant are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for energy and other factors, including the impacts of the COVID-19 pandemic, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year. Certain prior year data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the overall results of operations, financial position, or cash flows of any Registrant. Goodwill and Other Intangible Assets Goodwill at September 30, 2021 and December 31, 2020 was as follows: Goodwill (in millions) Southern Company $ 5,280 Southern Company Gas: Gas distribution operations $ 4,034 Gas marketing services 981 Southern Company Gas total $ 5,015 Goodwill is not amortized but is subject to an annual impairment test in the fourth quarter of the year and on an interim basis as events and changes in circumstances occur. Other intangible assets were as follows: At September 30, 2021 At December 31, 2020 Gross Carrying Amount Accumulated Amortization Other Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 212 $ (148) $ 64 $ 212 $ (135) $ 77 Trade names 64 (36) 28 64 (31) 33 Storage and transportation contracts () — — — 64 (64) — PPA fair value adjustments 390 (104) 286 390 (89) 301 Other 10 (8) 2 10 (9) 1 Total other intangible assets subject to amortization $ 676 $ (296) $ 380 $ 740 $ (328) $ 412 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 751 $ (296) $ 455 $ 815 $ (328) $ 487 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (104) $ 286 $ 390 $ (89) $ 301 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (128) $ 28 $ 156 $ (119) $ 37 Trade names 26 (14) 12 26 (12) 14 Wholesale gas services Storage and transportation contracts () — — — 64 (64) — Total other intangible assets subject to amortization $ 182 $ (142) $ 40 $ 246 $ (195) $ 51 (*) See Note (K) under "Southern Company Gas" for information regarding the sale of Sequent. Amortization associated with other intangible assets was as follows: Three Months Ended Nine Months Ended September 30, 2021 (in millions) Southern Company (a) $ 11 $ 33 Southern Power (b) 5 15 Southern Company Gas (c) 4 11 (a) Includes $5 million and $15 million for the three and nine months ended September 30, 2021, respectively, recorded as a reduction to operating revenues. (b) Recorded as a reduction to operating revenues. (c) Relates to gas marketing services. Cash, Cash Equivalents, and Restricted Cash The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amount shown in the condensed statements of cash flows for the applicable Registrants: Southern Southern Power Southern September 30, 2021 December 31, 2020 September 30, 2021 September 30, 2021 December 31, 2020 (in millions) (in millions) (in millions) Cash and cash equivalents $ 2,078 $ 1,065 $ 192 $ 29 $ 17 Restricted cash (a) : Other current assets 3 2 — 3 2 Other deferred charges and assets 21 — 21 — — Total cash, cash equivalents, and restricted cash (b) $ 2,101 $ 1,068 $ 213 $ 32 $ 19 (a) For Southern Company Gas, reflects restricted cash held as collateral for workers' compensation, life insurance, and long-term disability insurance. For Southern Power, reflects restricted cash held for construction payables. (b) Total may not add due to rounding. Natural Gas for Sale With the exception of Nicor Gas, Southern Company Gas records natural gas inventories on a WACOG basis. For any declines in market prices below the WACOG considered to be other than temporary, an adjustment is recorded to reduce the value of natural gas inventories to market value. Nicor Gas' natural gas inventory is carried at cost on a LIFO basis. Inventory decrements occurring during the year that are restored prior to year end are charged to cost of natural gas at the estimated annual replacement cost. Inventory decrements that are not restored prior to year end are charged to cost of natural gas at the actual LIFO cost of the inventory layers liquidated. Southern Company Gas recorded no material adjustments to natural gas inventories for any period presented. Nicor Gas' inventory decrement at September 30, 2021 is expected to be restored prior to year end. Asset Retirement Obligations See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. Details of changes in AROs for Southern Company, Alabama Power, Georgia Power, and Mississippi Power during the first nine months of 2021 are shown in the following table. There were no material changes in AROs for the other Registrants during the first nine months of 2021. Southern Company Alabama Power Georgia Mississippi Power (in millions) Balance at December 31, 2020 $ 10,684 $ 3,974 $ 6,265 $ 176 Liabilities incurred 17 — 3 — Liabilities settled (341) (152) (154) (18) Accretion 304 116 176 6 Cash flow revisions 945 385 475 30 Balance at September 30, 2021 $ 11,609 $ 4,323 $ 6,765 $ 194 In August 2021, Alabama Power recorded an increase of approximately $385 million to its AROs related to the CCR Rule and the related state rule based on updated estimates for post-closure costs at its ash ponds and inflation rates. In September 2021, Georgia Power recorded an increase of approximately $435 million to its AROs related to the CCR Rule and the related state rule based on updated estimates for inflation rates and the timing of closure activities. In September 2021, Mississippi Power recorded an increase of approximately $30 million to its AROs related to the CCR Rule based on updated estimates for the timing of closure activities, post-closure costs at one of its ash ponds, and inflation rates. The traditional electric operating companies have periodically updated, and expect to continue periodically updating, their related cost estimates and ARO liabilities for each CCR unit as additional information related to these assumptions becomes available. Some of these updates have been, and future updates may be, material. Additionally, the closure designs and plans in the States of Alabama and Georgia are subject to approval by environmental regulatory agencies. Absent continued recovery of ARO costs through regulated rates, results of operations, cash flows, and financial condition for Southern Company and the traditional electric operating companies could be materially impacted. See Note (B) under "Georgia Power – Rate Plan" for additional information. The ultimate outcome of these matters cannot be determined at this time.

Regulatory Matters

Regulatory Matters	9 Months Ended
Regulatory Matters	Sep. 30, 2021
Regulated Operations [Abstract]
Regulatory Matters	REGULATORY MATTERS See Note 2 to the financial statements in Item 8 of the Form 10-K for additional information relating to regulatory matters. The recovery balances for certain retail regulatory clauses of the traditional electric operating companies and Southern Company Gas at September 30, 2021 and December 31, 2020 were as follows: Regulatory Clause Balance Sheet Line Item September 30, December 31, 2020 (in millions) Alabama Power Rate CNP Compliance Other regulatory liabilities, current $ — $ 28 Other regulatory liabilities, deferred 24 — Rate CNP PPA Other regulatory assets, deferred 88 58 Retail Energy Cost Recovery Other regulatory liabilities, current — 18 Other regulatory assets, current 79 — Other regulatory assets, deferred 6 — Natural Disaster Reserve Other regulatory liabilities, deferred 36 77 Georgia Power Fuel Cost Recovery Over recovered fuel clause revenues $ — $ 113 Other deferred charges and assets 203 — Mississippi Power Fuel Cost Recovery Over recovered regulatory clause liabilities $ 5 $ 24 Ad Valorem Tax Other regulatory assets, current 12 11 Other regulatory assets, deferred 39 41 Property Damage Reserve Other regulatory liabilities, deferred — 4 Other regulatory assets, deferred 16 — Southern Company Gas Natural Gas Cost Recovery () Other regulatory liabilities $ — $ 88 Natural gas cost under recovery 432 — Other regulatory assets, deferred 79 — () The significant change during the nine months ended September 30, 2021 was primarily driven by an increase in the cost of gas purchased in February 2021 resulting from Winter Storm Uri. Alabama Power Certificate of Convenience and Necessity Energy Alabama, Gasp, Inc., and the Sierra Club filed requests for reconsideration and rehearing with the Alabama PSC regarding the certificate of convenience and necessity (CCN) issued to Alabama Power in August 2020, which authorized, among other things, the construction of Plant Barry Unit 8 and the acquisition of the Central Alabama Generating Station. In December 2020, the Alabama PSC issued an order denying the requests. On January 7, 2021, Energy Alabama and Gasp, Inc. filed a judicial appeal regarding both the Alabama PSC's August 2020 CCN order and the December 2020 order denying reconsideration and rehearing. On March 9, 2021, the Circuit Court of Montgomery County, Alabama granted a motion by Alabama Power to intervene in the appeal. On August 27, 2021, the court affirmed both the August 2020 and December 2020 Alabama PSC orders. On October 7, 2021, Energy Alabama and Gasp, Inc. filed an unopposed motion for voluntary dismissal of their direct appeal previously filed on January 7, 2021. This matter is now concluded. At September 30, 2021, expenditures associated with the construction of Plant Barry Unit 8 included in CWIP totaled approximately $222 million. Plant Greene County Alabama Power jointly owns Plant Greene County with an affiliate, Mississippi Power. See Note 5 under "Joint Ownership Agreements" in Item 8 of the Form 10-K for additional information. On September 9, 2021, the Mississippi PSC issued an order confirming the conclusion of its review of Mississippi Power's 2021 IRP with no deficiencies identified. Mississippi Power's 2021 IRP includes a schedule to retire Mississippi Power's 40% ownership interest in Plant Greene County Units 1 and 2 in December 2025 and 2026, respectively, consistent with each unit's remaining useful life. The Plant Greene County unit retirements identified by Mississippi Power require the completion of transmission and system reliability improvements, as well as agreement by Alabama Power. Alabama Power will continue to monitor the status of the transmission and system reliability improvements. Currently, Alabama Power plans to retire Plant Greene County Units 1 and 2 at the dates indicated. The ultimate outcome of this matter cannot be determined at this time. Rate NDR Based on an order from the Alabama PSC, when Alabama Power's NDR balance falls below $50 million, a reserve establishment charge will be activated and the ongoing reserve maintenance charge will be concurrently suspended until the NDR balance reaches $75 million. At September 30, 2021, Alabama Power's NDR balance was $36 million. Effective with October 2021 billings, the reserve maintenance charge component of Rate NDR was suspended and the reserve establishment charge was activated. Alabama Power expects to collect approximately $4 million in the fourth quarter 2021 and $16 million annually under Rate NDR until the NDR balance is restored to $75 million. Calhoun Generating Station Acquisition On September 23, 2021, Alabama Power entered into an agreement to acquire all of the equity interests in Calhoun Power Company, LLC, which owns and operates a 743-MW winter peak, simple-cycle, combustion turbine generation facility in Calhoun County, Alabama (Calhoun Generating Station). The total purchase price associated with the acquisition is approximately $180 million, subject to working capital adjustments. The completion of the acquisition is subject to the satisfaction and waiver of certain conditions, including, among other customary conditions, approval by the Alabama PSC and the FERC, as well as the expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act. Alabama Power expects to complete the transaction by September 30, 2022. On October 28, 2021, Alabama Power filed a petition for a CCN with the Alabama PSC to procure additional generating capacity through the acquisition of the Calhoun Generating Station. Upon certification, Alabama Power expects to recover costs associated with the Calhoun Generating Station through its existing rate structure, primarily Rate CNP New Plant, Rate CNP Compliance, Rate ECR, and Rate RSE. The ultimate outcome of this matter cannot be determined at this time. Georgia Power Rate Plan Effective January 1, 2021, Georgia Power reduced its amortization of costs associated with CCR AROs by approximately $90 million as approved by the Georgia PSC in conjunction with Georgia Power's annual compliance filings. In February 2020, the Georgia PSC denied a motion for reconsideration filed by the Sierra Club regarding the Georgia PSC's decision in the 2019 ARP allowing Georgia Power to recover compliance costs for CCR AROs, and, in December 2020, the Superior Court of Fulton County affirmed the decision of the Georgia PSC. On October 25, 2021, the Georgia Court of Appeals affirmed the Superior Court of Fulton County's December 2020 order. On November 3, 2021, the Sierra Club filed a motion for reconsideration with the Georgia Court of Appeals. The ultimate outcome of this matter cannot be determined at this time. In accordance with the terms of the 2019 ARP, on October 1, 2021, Georgia Power filed the following tariff adjustments to become effective January 1, 2022 pending approval by the Georgia PSC: • increase traditional base tariffs by approximately $192 million; • decrease the ECCR tariff by approximately $12 million; • decrease Demand-Side Management tariffs by approximately $25 million; and • increase Municipal Franchise Fee tariffs by approximately $2 million. The ultimate outcome of this matter cannot be determined at this time. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information regarding Georgia Power's AROs. Plant Vogtle Unit 3 and Common Facilities Rate Proceeding On June 15, 2021, Georgia Power filed an application with the Georgia PSC to adjust retail base rates to include the portion of costs related to its investment in Plant Vogtle Unit 3 and the common facilities shared between Plant Vogtle Units 3 and 4 (Common Facilities) previously deemed prudent by the Georgia PSC ($2.38 billion), as well as the related costs of operation. On November 2, 2021, the Georgia PSC voted to approve Georgia Power's application as filed, with the following modifications pursuant to a stipulated agreement between Georgia Power and the staff of the Georgia PSC. Georgia Power will include in rate base $2.1 billion of the $2.38 billion previously deemed prudent by the Georgia PSC and will recover the related depreciation expense through retail base rates. Financing costs on the remaining portion of the total Unit 3 and the Common Facilities construction costs will continue to be recovered through the NCCR tariff or deferred. Georgia Power will defer as a regulatory asset the remaining depreciation expense (approximately $38 million annually) until Unit 4 costs are placed in retail base rates. In addition, the stipulated agreement clarified that following the prudency review, the remaining amount to be placed in retail base rates will be net of the proceeds from the Guarantee Settlement Agreement and will not be used to offset imprudent costs, if any. The related increase in annual retail base rates of approximately $302 million also includes recovery of all projected operations and maintenance expenses for Unit 3 and the Common Facilities and other related costs of operation, partially offset by the related production tax credits, and will become effective the month after Unit 3 is placed in service. This increase will be partially offset by a decrease in the NCCR tariff of approximately $78 million expected to be effective January 1, 2022. See "Nuclear Construction" herein for additional information on Plant Vogtle Units 3 and 4. Deferral of Incremental COVID-19 Costs Since June 2021, Georgia Power has continued a review of bad debt amounts deferred under the Georgia PSC-approved methodology, including consideration of actual amounts repaid by customers from arrears and installment plans after the disconnection moratorium period ended in July 2020. As a result, Georgia Power has reduced the balance of deferred incremental costs by a total of approximately $23 million through September 30, 2021. At September 30, 2021, the incremental costs deferred totaled approximately $20 million, including approximately $1 million of incremental bad debt costs and $19 million of other incremental costs. The period over which these costs will be recovered is expected to be determined in Georgia Power's next base rate case. The ultimate outcome of this matter cannot be determined at this time. Fuel Cost Recovery Georgia Power has established fuel cost recovery rates approved by the Georgia PSC. On October 12, 2021, Georgia Power filed a notification and plan with the Georgia PSC to implement an interim fuel rider and increase Nuclear Construction In 2009, the Georgia PSC certified construction of Plant Vogtle Units 3 and 4, in which Georgia Power holds a 45.7% ownership interest. In 2012, the NRC issued the related combined construction and operating licenses, which allowed full construction of the two AP1000 nuclear units (with electric generating capacity of approximately 1,100 MWs each) and related facilities to begin. Until March 2017, construction on Plant Vogtle Units 3 and 4 continued under the Vogtle 3 and 4 Agreement, which was a substantially fixed price agreement. In connection with the EPC Contractor's bankruptcy filing in March 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, entered into several transitional arrangements to allow construction to continue. In July 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, entered into the Vogtle Services Agreement, whereby Westinghouse provides facility design and engineering services, procurement and technical support, and staff augmentation on a time and materials cost basis. The Vogtle Services Agreement provides that it will continue until the start-up and testing of Plant Vogtle Units 3 and 4 are complete and electricity is generated and sold from both units. The Vogtle Services Agreement is terminable by the Vogtle Owners upon 30 days' written notice. In October 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, executed the Bechtel Agreement, a cost reimbursable plus fee arrangement, whereby Bechtel is reimbursed for actual costs plus a base fee and an at-risk fee, which is subject to adjustment based on Bechtel's performance against cost and schedule targets. Each Vogtle Owner is severally (not jointly) liable for its proportionate share, based on its ownership interest, of all amounts owed to Bechtel under the Bechtel Agreement. The Vogtle Owners may terminate the Bechtel Agreement at any time for their convenience, provided that the Vogtle Owners will be required to pay amounts related to work performed prior to the termination (including the applicable portion of the base fee), certain termination-related costs, and, at certain stages of the work, the applicable portion of the at-risk fee. Bechtel may terminate the Bechtel Agreement under certain circumstances, including certain Vogtle Owner suspensions of work, certain breaches of the Bechtel Agreement by the Vogtle Owners, Vogtle Owner insolvency, and certain other events. See Note 8 to the financial statements under "Long-term Debt – DOE Loan Guarantee Borrowings" in Item 8 of the Form 10-K for information on the Amended and Restated Loan Guarantee Agreement, including applicable covenants, events of default, mandatory prepayment events, and conditions to borrowing. Cost and Schedule Georgia Power's approximate proportionate share of the remaining estimated capital cost to complete Plant Vogtle Units 3 and 4, including contingency, through September 2022 and June 2023, respectively, is as follows: (in millions) Base project capital cost forecast (a)(b) $ 9,342 Construction contingency estimate 137 Total project capital cost forecast (a)(b) 9,479 Net investment at September 30, 2021 (b) (8,159) Remaining estimate to complete $ 1,320 (a) Includes approximately $570 million of costs that are not shared with the other Vogtle Owners. Excludes financing costs expected to be capitalized through AFUDC of approximately $318 million, of which $169 million had been accrued through September 30, 2021. (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related customer refunds. Georgia Power estimates that its financing costs for construction of Plant Vogtle Units 3 and 4 will total approximately $3.2 billion, of which $2.8 billion had been incurred through September 30, 2021. As part of its ongoing processes, Southern Nuclear continues to evaluate cost and schedule forecasts on a regular basis to incorporate current information available, particularly in the areas of engineering support, commodity installation, system turnovers and related test results, and workforce statistics. Southern Nuclear establishes aggressive target values for monthly construction production and system turnover activities. Southern Nuclear's site work plans continue to reflect this approach in support of safely completing Units 3 and 4, while achieving the required construction quality. In mid-March 2020, Southern Nuclear began implementing policies and procedures designed to mitigate the risk of transmission of COVID-19 at the construction site, including worker distancing measures; isolating individuals who tested positive for COVID-19, showed symptoms consistent with COVID-19, were being tested for COVID-19, or were in close contact with such persons; requiring self-quarantine; and adopting additional precautionary measures. Since March 2020, the number of active cases at the site has fluctuated and impacted productivity levels and pace of activity completion. Through June 2021, the site experienced an overall decline in the number of active cases since the peak in January 2021. During the third quarter 2021, the site experienced a similar peak in August 2021; however, the number of active cases since this peak has declined. The lower productivity levels and slower pace of activity completion experienced since March 2020 contributed to a backlog to the aggressive site work plan established at the beginning of 2020. Georgia Power estimates the productivity impacts of the COVID-19 pandemic have consumed approximately three Following the January 2021 milestone extensions, Southern Nuclear has been performing additional construction remediation work necessary to ensure quality and design standards are met as system turnovers are completed to support hot functional testing, which was completed in July 2021, and fuel load for Unit 3. As a result of challenges including, but not limited to, construction productivity, construction remediation work, the pace of system turnovers, spent fuel pool repairs, and the timeframe and duration for hot functional and other testing, at the end of the second quarter 2021, Southern Nuclear further extended certain milestone dates, including the fuel load for Unit 3, from those established in January 2021. Through the third quarter 2021, the project continued to face challenges including, but not limited to, construction productivity, construction remediation work, and the pace of system turnovers. As a result of these continued challenges, at the end of the third quarter 2021, Southern Nuclear further extended certain milestone dates, including fuel load for Unit 3, from those established at the end of the second quarter 2021. The site work plan currently targets fuel load for Unit 3 in the first quarter 2022 and an in-service date of May 2022 and primarily depends on significant improvements in overall construction productivity and production levels, the volume of construction remediation work, the pace of system and area turnovers, and the progression of startup and other testing. As the site work plan includes minimal margin to these milestone dates, an in-service date in the third quarter 2022 for Unit 3 is projected, although any further delays could result in a later in-service date. As the result of productivity challenges, at the end of the second quarter 2021, Southern Nuclear also further extended milestone dates for Unit 4 from those established in January 2021. These productivity challenges continued into the third quarter 2021 and some craft and support resources were diverted temporarily to support construction efforts on Unit 3. As a result of these factors, at the end of the third quarter 2021, Southern Nuclear further extended the milestone dates for Unit 4 from those established at the end of the second quarter 2021. The site work plan targets an in-service date of March 2023 for Unit 4 and primarily depends on overall construction productivity and production levels significantly improving as well as appropriate levels of craft laborers, particularly electricians and pipefitters, being added and maintained. As the site work plan includes minimal margin to the milestone dates, an in-service date in the second quarter 2023 for Unit 4 is projected, although any further delays could result in a later in-service date. As of March 31, 2021, approximately $84 million of the construction contingency established in the fourth quarter 2020 was assigned to the base capital cost forecast for costs primarily associated with the schedule extension for Unit 3 to December 2021, construction productivity, support resources, and construction remediation work. Georgia Power increased its total capital cost forecast as of March 31, 2021 by adding $48 million to the remaining construction contingency. As of June 30, 2021, all of the remaining construction contingency previously established and an additional $341 million was assigned to the base capital cost forecast for costs primarily associated with the schedule extensions for Units 3 and 4, construction remediation work for Unit 3, and construction productivity and support resources for Units 3 and 4. Georgia Power also increased its total capital cost forecast as of June 30, 2021 by adding $119 million to replenish construction contingency. As a result of the factors discussed above, during the third quarter 2021, all of the remaining construction contingency previously established in the second quarter 2021 and an additional $127 million was assigned to the base capital cost forecast for costs primarily associated with the schedule extensions for Units 3 and 4, construction productivity and support resources for Units 3 and 4, and construction remediation work for Unit 3. Georgia Power also increased its total capital cost forecast as of September 30, 2021 by adding $137 million to replenish construction contingency. After considering the significant level of uncertainty that exists regarding the future recoverability of these costs since the ultimate outcome of these matters is subject to the outcome of future assessments by management, as well as Georgia PSC decisions in future regulatory proceedings, Georgia Power recorded pre-tax charges to income in the first quarter 2021, the second quarter 2021, and the third quarter 2021 of $48 million ($36 million after tax), $460 million ($343 million after tax), and $264 million ($197 million after tax), respectively, for the increases in the total project capital cost forecast. As and when these amounts are spent, Georgia Power may request the Georgia PSC to evaluate those expenditures for rate recovery. In addition, the continuing effects of the COVID-19 pandemic could further disrupt or delay construction and testing activities at Plant Vogtle Units 3 and 4. Georgia Power's proportionate share of the estimated incremental cost associated with COVID-19 mitigation actions and impacts on construction productivity is currently estimated to be between $160 million and $200 million and is included in the total project capital cost forecast. As construction, including subcontract work, continues and testing and system turnover activities increase, ongoing or future challenges with management of contractors and vendors; subcontractor performance; supervision of craft labor and related productivity, particularly in the installation of electrical, mechanical, and instrumentation and controls commodities, ability to attract and retain craft labor, and/or related cost escalation; procurement, fabrication, delivery, assembly, installation, system turnover, and the initial testing and start-up, including any required engineering changes or any remediation related thereto, of plant systems, structures, or components (some of which are based on new technology that only within the last few years began initial operation in the global nuclear industry at this scale), including the spent fuel pools, any of which may require additional labor and/or materials; or other issues could continue or arise and change the projected schedule and estimated cost. There have been technical and procedural challenges to the construction and licensing of Plant Vogtle Units 3 and 4 at the federal and state level and additional challenges may arise. Processes are in place that are designed to ensure compliance with the requirements specified in the Westinghouse Design Control Document and the combined construction and operating licenses, including inspections by Southern Nuclear and the NRC that occur throughout construction. In connection with the additional construction remediation work described above, Southern Nuclear reviewed the project's construction quality programs and, where needed, is implementing improvement plans consistent with these processes. In June 2021, the NRC began a special inspection to review the root cause of this additional construction remediation work and the corresponding corrective action plans. On August 26, 2021, the NRC issued an inspection report with initial findings. Southern Nuclear had already identified and self-reported many of the issues in this report to the NRC and implemented corrective-action plans to resolve these issues. Southern Nuclear responded to the NRC's initial findings on October 5, 2021 and expects a final report from the NRC by November 24, 2021. Findings resulting from this or other inspections could require additional remediation and/or further NRC oversight. In addition, certain license amendment requests have been filed and approved or are pending before the NRC. On March 15, 2021, the NRC denied the Blue Ridge Environmental Defense League's (BREDL) December 2020 motion to reopen proceedings on BREDL's petition challenging a requested license amendment, which has been issued by the NRC staff. The site work plan currently targets fuel load for Unit 3 in the first quarter 2022. Various design and other licensing-based compliance matters, including the timely submittal by Southern Nuclear of the ITAAC documentation for each unit and the related reviews and approvals by the NRC necessary to support NRC authorization to load fuel, have arisen or may arise, which may result in additional license amendments or require other resolution. If any license amendment requests or other licensing-based compliance issues, including inspections and ITAACs, are not resolved in a timely manner, there may be delays in the project schedule that could result in increased costs. The ultimate outcome of these matters cannot be determined at this time. However, any extension of the in-service date beyond the third quarter 2022 for Unit 3 or the second quarter 2023 for Unit 4 is currently estimated to result in additional base capital costs for Georgia Power of approximately $25 million per month for Unit 3 and approximately $15 million per month for Unit 4, as well as the related AFUDC and any additional related construction or testing costs. While Georgia Power is not precluded from seeking recovery of any future capital cost forecast increase, management will ultimately determine whether or not to seek recovery. Any further changes to the capital cost forecast that are not expected to be recoverable through regulated rates will be required to be charged to income and such charges could be material. Joint Owner Contracts In November 2017, the Vogtle Owners entered into an amendment to their joint ownership agreements for Plant Vogtle Units 3 and 4 to provide for, among other conditions, additional Vogtle Owner approval requirements. Effective in August 2018, the Vogtle Owners further amended the joint ownership agreements to clarify and provide procedures for certain provisions of the joint ownership agreements related to adverse events that require the vote of the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 to continue construction (as amended, and together with the November 2017 amendment, the Vogtle Joint Ownership Agreements). The Vogtle Joint Ownership Agreements also confirm that the Vogtle Owners' sole recourse against Georgia Power or Southern Nuclear for any action or inaction in connection with their performance as agent for the Vogtle Owners is limited to removal of Georgia Power and/or Southern Nuclear as agent, except in cases of willful misconduct. As a result of an increase in the total project capital cost forecast and Georgia Power's decision not to seek rate recovery of the increase in the base capital costs in conjunction with the nineteenth VCM report in 2018, the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 were required to vote to continue construction. In September 2018, the Vogtle Owners unanimously voted to continue construction of Plant Vogtle Units 3 and 4. Amendments to the Vogtle Joint Ownership Agreements In connection with the vote to continue construction, Georgia Power entered into (i) a binding term sheet (Vogtle Owner Term Sheet) with the other Vogtle Owners and MEAG Power's wholly-owned subsidiaries MEAG Power SPVJ, LLC (MEAG SPVJ), MEAG Power SPVM, LLC (MEAG SPVM), and MEAG Power SPVP, LLC (MEAG SPVP) to take certain actions which partially mitigate potential financial exposure for the other Vogtle Owners, including additional amendments to the Vogtle Joint Ownership Agreements and the purchase of PTCs from the other Vogtle Owners at pre-established prices, and (ii) a term sheet (MEAG Term Sheet) with MEAG Power and MEAG SPVJ to provide up to $300 million of funding with respect to MEAG SPVJ's ownership interest in Plant Vogtle Units 3 and 4 under certain circumstances. In January 2019, Georgia Power, MEAG Power, and MEAG SPVJ entered into an agreement to implement the provisions of the MEAG Term Sheet. In February 2019, Georgia Power, the other Vogtle Owners, and MEAG Power's wholly-owned subsidiaries MEAG SPVJ, MEAG SPVM, and MEAG SPVP entered into certain amendments to the Vogtle Joint Ownership Agreements to implement the provisions of the Vogtle Owner Term Sheet (Global Amendments). As previously disclosed, pursuant to the Global Amendments: (i) each Vogtle Owner must pay its proportionate share of qualifying construction costs for Plant Vogtle Units 3 and 4 based on its ownership percentage up to the estimated cost at completion (EAC) for Plant Vogtle Units 3 and 4 which formed the basis of Georgia Power's forecast of $8.4 billion in the nineteenth VCM plus $800 million; (ii) Georgia Power will be responsible for 55.7% of actual qualifying construction costs between $800 million and $1.6 billion over the EAC in the nineteenth VCM (resulting in $80 million of potential additional costs to Georgia Power), with the remaining Vogtle Owners responsible for 44.3% of such costs pro rata in accordance with their respective ownership interests; and (iii) Georgia Power will be responsible for 65.7% of qualifying construction costs between $1.6 billion and $2.1 billion over the EAC in the nineteenth VCM (resulting in a further $100 million of potential additional costs to Georgia Power), with the remaining Vogtle Owners responsible for 34.3% of such costs pro rata in accordance with their respective ownership interests. If the EAC is revised and exceeds the EAC in the nineteenth VCM by more than $2.1 billion, each of the other Vogtle Owners will have a one-time option at the time the project budget forecast is so revised to tender a portion of its ownership interest to Georgia Power in exchange for Georgia Power's agreement to pay 100% of such Vogtle Owner's remaining share of total construction costs in excess of the EAC in the nineteenth VCM plus $2.1 billion. In addition, pursuant to the Global Amendments, the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 must vote to continue construction if certain adverse events occur, including, among other events: (i) the bankruptcy of Toshiba; (ii) the termination or rejection in bankruptcy of certain agreements, including the Vogtle Services Agreement, the Bechtel Agreement, or the agency agreement with Southern Nuclear; (iii) Georgia Power's public announcement of its intention not to submit for rate recovery any portion of its investment in Plant Vogtle Units 3 and 4 or the Georgia PSC determines that any of Georgia Power's costs relating to the construction of Plant Vogtle Units 3 and 4 will not be recovered in retail rates, excluding any additional amounts paid by Georgia Power on behalf of the other Vogtle Owners pursuant to the Global Amendments described above and the first 6% of costs during any six-month VCM reporting period that are disallowed by the Georgia PSC for recovery, or for which Georgia Power elects not to seek cost recovery, through retail rates; and (iv) an incremental extension of one year or more over the most recently approved schedule. Georgia Power and the other Vogtle Owners do not agree on either the starting dollar amount for the determination of cost increases subject to the cost-sharing and tender provisions of the Global Amendments or the extent to which COVID-19-related costs impact the calculation. Based on the definition in the Global Amendments, Georgia Power believes the starting dollar amount is $18.38 billion and does not believe estimated project costs have reached a level where cost-sharing would be triggered. However, the other Vogtle Owners have asserted the cost increases through September 30, 2021 have reached the cost-sharing thresholds and could be sufficient to trigger the tender provisions under the Global Amendments, which could require Georgia Power to record additional pre-tax charges to income of up to approximately $350 million. On October 29, 2021, Georgia Power and the other Vogtle Owners entered into an agreement to clarify the process for the tender provisions of the Global Amendments, which will provide additional time to resolve these matters. The ultimate outcome of these matters cannot be determined at this time. Regulatory Matters In 2009, the Georgia PSC voted to certify construction of Plant Vogtle Units 3 a

Contingencies

Contingencies	9 Months Ended
Contingencies	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingencies	CONTINGENCIESSee Note 3 to the financial statements in Item 8 of the Form 10-K for information relating to various lawsuits and other contingencies. General Litigation Matters The Registrants are involved in various matters being litigated and regulatory matters. The ultimate outcome of such pending or potential litigation or regulatory matters against each Registrant and any subsidiaries cannot be determined at this time; however, for current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on such Registrant's financial statements. The Registrants believe the pending legal challenges discussed below have no merit; however, the ultimate outcome of these matters cannot be determined at this time. Southern Company In February 2017, Jean Vineyard and Judy Mesirov each filed a shareholder derivative lawsuit in the U.S. District Court for the Northern District of Georgia. Each of these lawsuits names as defendants Southern Company, certain of its directors, certain of its current and former officers, and certain former Mississippi Power officers. In 2017, these two shareholder derivative lawsuits were consolidated in the U.S. District Court for the Northern District of Georgia. The complaints allege that the defendants caused Southern Company to make false or misleading statements regarding the Kemper County energy facility cost and schedule. Further, the complaints allege that the defendants were unjustly enriched and caused the waste of corporate assets and also allege that the individual defendants violated their fiduciary duties. In May 2017, Helen E. Piper Survivor's Trust filed a shareholder derivative lawsuit in the Superior Court of Gwinnett County, Georgia that names as defendants Southern Company, certain of its directors, certain of its current and former officers, and certain former Mississippi Power officers. The complaint alleges that the individual defendants, among other things, breached their fiduciary duties in connection with schedule delays and cost overruns associated with the construction of the Kemper County energy facility. The complaint further alleges that the individual defendants authorized or failed to correct false and misleading statements regarding the Kemper County energy facility schedule and cost and failed to implement necessary internal controls to prevent harm to Southern Company. In August 2019, the court granted a motion filed by the plaintiff in July 2019 to substitute a new named plaintiff, Martin J. Kobuck, in place of Helen E. Piper Survivor's Trust. The plaintiffs in each of these cases seek to recover, on behalf of Southern Company, unspecified actual damages and, on each plaintiff's own behalf, attorneys' fees and costs in bringing the lawsuit. The plaintiffs also seek certain changes to Southern Company's corporate governance and internal processes. In 2018, the court in each case entered an order staying each lawsuit until 30 days after the settlement of a securities class action filed in January 2017 against Southern Company, certain of its current and former officers, and certain former Mississippi Power officers. In September 2020, the plaintiffs in each case filed a status report noting the settlement of the securities class action and informing the court that the parties had scheduled mediation, which occurred in November 2020. In September 2021, the parties executed a term sheet memorializing a settlement-in-principle of both pending derivative lawsuits. The parties are negotiating a global stipulation of settlement that will apply to both lawsuits and will be subject to approval by the federal court. If approved, the terms of the settlement-in-principle are not expected to have a material impact on Southern Company's financial statements. Georgia Power In 2011, plaintiffs filed a putative class action against Georgia Power in the Superior Court of Fulton County, Georgia alleging that Georgia Power's collection in rates of amounts for municipal franchise fees (which fees are paid to municipalities) exceeded the amounts allowed in orders of the Georgia PSC and alleging certain state law claims. This case has been ruled upon and appealed numerous times over the last several years. In one recent appeal, the Georgia Supreme Court remanded the case and noted that the trial court could refer the matter to the Georgia PSC to interpret its tariffs. Following a motion by Georgia Power, in February 2019, the Superior Court of Fulton County ordered the parties to submit petitions to the Georgia PSC for a declaratory ruling and also conditionally certified the proposed class. In March 2019, Georgia Power and the plaintiffs filed petitions with the Georgia PSC seeking confirmation of the proper application of the municipal franchise fee schedule pursuant to the Georgia PSC's orders. Also in March 2019, Georgia Power appealed the class certification decision to the Georgia Court of Appeals. In October 2019, the Georgia PSC issued an order that found Georgia Power has appropriately implemented the municipal franchise fee schedule. In March 2020, the Georgia Court of Appeals vacated the Superior Court of Fulton County's February 2019 order granting conditional class certification and remanded the case to the Superior Court of Fulton County for further proceedings. In September 2020, the plaintiffs and Georgia Power each filed motions for summary judgment and the plaintiffs renewed their motion for class certification. On March 16, 2021, the Superior Court of Fulton County granted class certification and Georgia Power's motion for summary judgment. On March 22, 2021, the plaintiffs filed a notice of appeal, and, on April 2, 2021, Georgia Power filed a notice of cross appeal on the issue of class certification. The amount of any possible losses cannot be estimated at this time because, among other factors, it is unknown whether any losses would be subject to recovery from any municipalities. In July 2020, a group of individual plaintiffs filed a complaint in the Superior Court of Fulton County, Georgia against Georgia Power alleging that releases from Plant Scherer have impacted groundwater, surface water, and air, resulting in alleged personal injuries and property damage. The plaintiffs seek an unspecified amount of monetary Mississippi Power In 2018, Ray C. Turnage and 10 other individual plaintiffs filed a putative class action complaint against Mississippi Power and the three then-serving members of the Mississippi PSC in the U.S. District Court for the Southern District of Mississippi. Mississippi Power received Mississippi PSC approval in 2013 to charge a mirror CWIP rate premised upon including in its rate base pre-construction and construction costs for the Kemper IGCC prior to placing the Kemper IGCC into service. The Mississippi Supreme Court reversed that approval and ordered Mississippi Power to refund the amounts paid by customers under the previously-approved mirror CWIP rate. The plaintiffs allege that the initial approval process, and the amount approved, were improper. They also allege that Mississippi Power underpaid customers by up to $23.5 million in the refund process by applying an incorrect interest rate. The plaintiffs seek to recover, on behalf of themselves and their putative class, actual damages, punitive damages, pre-judgment interest, post-judgment interest, attorney's fees, and costs. In response to Mississippi Power and the Mississippi PSC each filing a motion to dismiss, the plaintiffs filed an amended complaint in March 2019. The amended complaint included four additional plaintiffs and additional claims for gross negligence, reckless conduct, and intentional wrongdoing. Mississippi Power and the Mississippi PSC each filed a motion to dismiss the amended complaint, which occurred in May 2020 and March 2020, respectively. Also in March 2020, the plaintiffs filed a motion seeking to name the new members of the Mississippi PSC, the Mississippi Development Authority, and Southern Company as additional defendants and add a cause of action against all defendants based on a dormant commerce clause theory under the U.S. Constitution. In July 2020, the plaintiffs filed a motion for leave to file a third amended complaint, which included the same federal claims as the proposed second amended complaint, as well as several additional state law claims based on the allegation that Mississippi Power failed to disclose the annual percentage rate of interest applicable to refunds. In November 2020, the court denied each of the plaintiffs' pending motions and entered final judgment in favor of Mississippi Power. On January 22, 2021, the court denied further motions by the plaintiffs to vacate the judgment and to file a revised second amended complaint. On February 19, 2021, the plaintiffs filed a notice of appeal with the U.S. Court of Appeals for the Fifth Circuit. An adverse outcome in this proceeding could have a material impact on Mississippi Power's financial statements. See Note 3 to the financial statements under "Other Matters – Mississippi Power – Kemper County Energy Facility" in Item 8 of the Form 10-K for additional information. Environmental Remediation The Southern Company system must comply with environmental laws and regulations governing the handling and disposal of waste and releases of hazardous substances. Under these various laws and regulations, the Southern Company system could incur substantial costs to clean up affected sites. The traditional electric operating companies and the natural gas distribution utilities in Illinois and Georgia have each received authority from their respective state PSCs or other applicable state regulatory agencies to recover approved environmental remediation costs through regulatory mechanisms. These regulatory mechanisms are adjusted annually or as necessary within limits approved by the state PSCs or other applicable state regulatory agencies. Georgia Power's environmental remediation liability was $19 million and $15 million at September 30, 2021 and December 31, 2020, respectively. Georgia Power has been designated or identified as a potentially responsible party at sites governed by the Georgia Hazardous Site Response Act and/or by the federal Comprehensive Environmental Response, Compensation, and Liability Act, and assessment and potential cleanup of such sites is expected. Southern Company Gas' environmental remediation liability was $255 million and $245 million at September 30, 2021 and December 31, 2020, respectively, based on the estimated cost of environmental investigation and remediation associated with known former manufactured gas plant operating sites. The ultimate outcome of these matters cannot be determined at this time; however, as a result of the regulatory treatment for environmental remediation expenses described above, the final disposition of these matters is not expected to have a material impact on the financial statements of the applicable Registrants. Southern Company Gas PennEast Pipeline Project On June 29, 2021, the U.S. Supreme Court ruled in favor of PennEast Pipeline regarding its federal eminent domain authority over lands in which a state has property rights interests. Southern Company Gas tests its equity method investments for impairment whenever events or changes in circumstances indicate that the investment may be impaired. Following the U.S. Supreme Court ruling, during the second quarter 2021, Southern Company Gas management reassessed the project construction timing, including the anticipated timing for receipt of the FERC certificate and all remaining state and local permits for both Phase 1 (the construction of 68 miles of pipe entirely within Pennsylvania) and Phase 2 (the construction of the remaining 50 miles in Pennsylvania and New Jersey), as well as potential challenges thereto, and performed an impairment analysis. The outcome of the analysis resulted in a pre-tax impairment charge of $82 million ($58 million after tax). On September 27, 2021, PennEast Pipeline announced that further development of the project is no longer supported, and, as a result, all further development of the project has ceased. During the third quarter 2021, Southern Company Gas recorded a pre-tax charge of $2 million ($2 million after tax) related to its share of the project level impairment, as well as $7 million of additional tax expense, resulting in total pre-tax charges of $84 million ($67 million after tax) during 2021 related to the project. See Note (E) under "Southern Company Gas" for additional information. SNG As a 50% equity investor in SNG, Southern Company Gas is required to make additional capital contributions as necessary pursuant to the terms of its operating agreement with SNG. Southern Company Gas previously committed to fund up to $150 million as a contingent capital contribution if SNG was unable to refinance or otherwise satisfy $300 million of debt maturing in June 2021. On April 29, 2021, SNG successfully refinanced the debt obligation. See Note (E) under "Southern Company Gas" for additional information.

Revenue from Contracts with Cus

Revenue from Contracts with Customers and Lease Income	9 Months Ended
Revenue from Contracts with Customers and Lease Income	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers and Lease Income	REVENUE FROM CONTRACTS WITH CUSTOMERS AND LEASE INCOME Revenue from Contracts with Customers The Registrants generate revenues from a variety of sources, some of which are not accounted for as revenue from contracts with customers, such as leases, derivatives, and certain cost recovery mechanisms. See Note 1 to the financial statements under "Revenues" in Item 8 of the Form 10-K for additional information on the revenue policies of the Registrants. See "Lease Income" herein and Note (J) for additional information on revenue accounted for under lease and derivative accounting guidance, respectively. The following table disaggregates revenue from contracts with customers for the three and nine months ended September 30, 2021 and 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2021 Operating revenues Retail electric revenues Residential $ 1,974 $ 750 $ 1,138 $ 86 $ — $ — Commercial 1,432 471 882 79 — — Industrial 902 394 428 80 — — Other 24 4 18 2 — — Total retail electric revenues 4,332 1,619 2,466 247 — — Natural gas distribution revenues Residential 218 — — — — 218 Commercial 55 — — — — 55 Transportation 239 — — — — 239 Industrial 6 — — — — 6 Other 31 — — — — 31 Total natural gas distribution revenues 549 — — — — 549 Wholesale electric revenues PPA energy revenues 359 61 41 2 261 — PPA capacity revenues 125 14 14 1 97 — Non-PPA revenues 63 54 3 120 134 — Total wholesale electric revenues 547 129 58 123 492 — Other natural gas revenues Gas marketing services 45 — — — — 45 Other natural gas revenues 11 — — — — 11 Total natural gas revenues 56 — — — — 56 Other revenues 248 53 112 8 9 — Total revenue from contracts with customers 5,732 1,801 2,636 378 501 605 Other revenue sources (a) 506 103 220 — 178 18 Total operating revenues $ 6,238 $ 1,904 $ 2,856 $ 378 $ 679 $ 623 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Nine Months Ended September 30, 2021 Operating revenues Retail electric revenues Residential $ 4,910 $ 1,931 $ 2,765 $ 214 $ — $ — Commercial 3,727 1,229 2,293 205 — — Industrial 2,299 1,048 1,034 217 — — Other 70 13 51 6 — — Total retail electric revenues 11,006 4,221 6,143 642 — — Natural gas distribution revenues Residential 1,143 — — — — 1,143 Commercial 298 — — — — 298 Transportation 775 — — — — 775 Industrial 29 — — — — 29 Other 187 — — — — 187 Total natural gas distribution revenues 2,432 — — — — 2,432 Wholesale electric revenues PPA energy revenues 782 143 71 9 575 — PPA capacity revenues 375 86 41 4 247 — Non-PPA revenues 181 108 14 283 273 — Total wholesale electric revenues 1,338 337 126 296 1,095 — Other natural gas revenues Wholesale gas services 2,168 — — — — 2,168 Gas marketing services 303 — — — — 303 Other natural gas revenues 27 — — — — 27 Total natural gas revenues 2,498 — — — — 2,498 Other revenues 792 150 362 22 18 — Total revenue from contracts with customers 18,066 4,708 6,631 960 1,113 4,930 Other revenue sources (a) 2,979 311 419 28 497 1,763 Other adjustments (b) (3,699) — — — — (3,699) Total operating revenues $ 17,346 $ 5,019 $ 7,050 $ 988 $ 1,610 $ 2,994 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2020 Operating revenues Retail electric revenues Residential $ 2,019 $ 752 $ 1,183 $ 84 $ — $ — Commercial 1,354 447 833 74 — — Industrial 783 358 352 73 — — Other 22 5 15 2 — — Total retail electric revenues 4,178 1,562 2,383 233 — — Natural gas distribution revenues Residential 170 — — — — 170 Commercial 41 — — — — 41 Transportation 224 — — — — 224 Industrial 4 — — — — 4 Other 35 — — — — 35 Total natural gas distribution revenues 474 — — — — 474 Wholesale electric revenues PPA energy revenues 214 40 13 2 165 — PPA capacity revenues 136 26 15 1 95 — Non-PPA revenues 59 10 3 93 68 — Total wholesale electric revenues 409 76 31 96 328 — Other natural gas revenues Wholesale gas services 431 — — — — 431 Gas marketing services 38 — — — — 38 Other natural gas revenues 7 — — — — 7 Total natural gas revenues 476 — — — — 476 Other revenues 218 33 115 6 4 — Total revenue from contracts with customers 5,755 1,671 2,529 335 332 950 Other revenue sources (a) 968 58 88 1 191 630 Other adjustments (b) (1,103) — — — — (1,103) Total operating revenues $ 5,620 $ 1,729 $ 2,617 $ 336 $ 523 $ 477 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Nine Months Ended September 30, 2020 Operating revenues Retail electric revenues Residential $ 4,802 $ 1,839 $ 2,760 $ 203 $ — $ — Commercial 3,589 1,152 2,242 195 — — Industrial 2,081 956 907 218 — — Other 68 16 46 6 — — Total retail electric revenues 10,540 3,963 5,955 622 — — Natural gas distribution revenues Residential 906 — — — — 906 Commercial 229 — — — — 229 Transportation 723 — — — — 723 Industrial 21 — — — — 21 Other 179 — — — — 179 Total natural gas distribution revenues 2,058 — — — — 2,058 Wholesale electric revenues PPA energy revenues 550 94 38 7 425 — PPA capacity revenues 339 78 30 3 231 — Non-PPA revenues 159 33 7 235 184 — Total wholesale electric revenues 1,048 205 75 245 840 — Other natural gas revenues Wholesale gas services 1,168 — — — — 1,168 Gas marketing services 258 — — — — 258 Other natural gas revenues 22 — — — — 22 Total natural gas revenues 1,448 — — — — 1,448 Other revenues 677 117 329 19 11 — Total revenue from contracts with customers 15,771 4,285 6,359 886 851 3,506 Other revenue sources (a) 2,604 160 12 9 486 1,973 Other adjustments (b) (3,117) — — — — (3,117) Total operating revenues $ 15,258 $ 4,445 $ 6,371 $ 895 $ 1,337 $ 2,362 (a) Other revenue sources relate to revenues from customers accounted for as derivatives and leases, alternative revenue programs at Southern Company Gas, and cost recovery mechanisms and revenues that meet other scope exceptions for revenues from contracts with customers at the traditional electric operating companies. (b) Other adjustments relate to the cost of Southern Company Gas' energy and risk management activities. Wholesale gas services revenues are presented net of the related costs of those activities on the statement of income. See Notes (K) and (L) under "Southern Company Gas" for information on the sale of Sequent and components of wholesale gas services' operating revenues, respectively. Contract Balances The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers at September 30, 2021 and December 31, 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivable At September 30, 2021 $ 2,343 $ 712 $ 904 $ 90 $ 170 $ 329 At December 31, 2020 2,614 632 806 77 112 788 Contract Assets At September 30, 2021 $ 165 $ 5 $ 103 $ — $ 1 $ — At December 31, 2020 158 2 71 — — — Contract Liabilities At September 30, 2021 $ 65 $ 6 $ 39 $ 1 $ 2 $ — At December 31, 2020 61 6 27 1 1 1 At September 30, 2021 and December 31, 2020, Georgia Power had contract assets primarily related to fixed retail customer bill programs, where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over a one-year contract term, and unregulated service agreements, where payment is contingent on project completion. Contract liabilities for Georgia Power relate to cash collections recognized in advance of revenue for unregulated service agreements. Southern Company's unregulated distributed generation business had $55 million and $81 million of contract assets and $19 million and $27 million of contract liabilities at September 30, 2021 and December 31, 2020, respectively, for outstanding performance obligations. Revenues recognized by Southern Company in the three and nine months ended September 30, 2021, which were included in contract liabilities at December 31, 2020, were $5 million and $25 million, respectively, and immaterial for all other Registrants. Remaining Performance Obligations The traditional electric operating companies and Southern Power have long-term contracts with customers in which revenues are recognized as performance obligations are satisfied over the contract term. These contracts primarily relate to PPAs whereby the traditional electric operating companies and Southern Power provide electricity and generation capacity to a customer. The revenue recognized for the delivery of electricity is variable; however, certain PPAs include a fixed payment for fixed generation capacity over the term of the contract. Southern Company's unregulated distributed generation business also has partially satisfied performance obligations related to certain fixed price contracts. Revenues from contracts with customers related to these performance obligations remaining at September 30, 2021 are expected to be recognized as follows: 2021 (remaining) 2022 2023 2024 2025 Thereafter (in millions) Southern Company $ 156 $ 543 $ 347 $ 327 $ 307 $ 2,667 Alabama Power 13 32 24 7 5 — Georgia Power 22 64 43 23 21 41 Southern Power 70 323 281 297 281 2,644 Lease Income Lease income for the three and nine months ended September 30, 2021 and 2020 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) For the Three Months Ended September 30, 2021 Lease income - interest income on sales-type leases $ 4 $ — $ — $ 4 $ — $ — Lease income - operating leases 56 21 11 — 21 9 Variable lease income 143 — — — 151 — Total lease income $ 203 $ 21 $ 11 $ 4 $ 172 $ 9 For the Nine Months Ended September 30, 2021 Lease income - interest income on sales-type leases $ 11 $ — $ — $ 10 $ — $ — Lease income - operating leases 168 62 31 1 64 26 Variable lease income 355 — — — 379 — Total lease income $ 534 $ 62 $ 31 $ 11 $ 443 $ 26 For the Three Months Ended September 30, 2020 Lease income - interest income on sales-type leases $ 3 $ — $ — $ 3 $ — $ — Lease income - operating leases 50 11 14 — 21 9 Variable lease income 145 — — — 153 — Total lease income $ 198 $ 11 $ 14 $ 3 $ 174 $ 9 For the Nine Months Ended September 30, 2020 Lease income - interest income on sales-type leases $ 8 $ — $ — $ 8 $ — $ — Lease income - operating leases 148 24 44 1 66 26 Variable lease income 345 — — — 368 — Total lease income $ 501 $ 24 $ 44 $ 9 $ 434 $ 26 Lease payments received under tolling arrangements and PPAs consist of either scheduled payments or variable payments based on the amount of energy produced by the underlying electric generating units. Lease income for Alabama Power and Southern Power is included in wholesale revenues. Lease Receivables Mississippi Power Mississippi Power completed construction of additional leased assets under an existing sales-type lease during the second quarter 2021. Upon completion of construction, the book value was transferred from CWIP to lease receivables. At September 30, 2021, the lease receivable related to the additional leased assets totaled $39 million and is primarily included in other property and investments. The transfer represents a noncash investing transaction for purposes of the statements of cash flows. Southern Power During the third quarter 2021, Southern Power completed construction of a portion of the Garland battery energy storage facility assets and recorded a $15 million loss upon commencement of the related PPA, which Southern Power accounts for as a sales-type lease. The lease has an initial term of 20 years. Upon commencement of the lease, the $113 million book value of the assets was derecognized from CWIP and a lease receivable was recorded. At September 30, 2021, the current portion of the lease receivable of $8 million is included in other current assets and the long-term portion of $91 million is included in net investment in sales-type lease on the balance sheet. The transfer represented a noncash investing transaction for purposes of the statement of cash flows. The undiscounted cash flows expected to be received by Southern Power for assets under the lease are as follows: At September 30, 2021 (in millions) 2021 (remaining) $ 2 2022 8 2023 8 2024 8 2025 8 2026 8 Thereafter 115 Total undiscounted cash flows $ 157 Net investment in sales-type lease () 99 Difference between undiscounted cash flows and discounted cash flows $ 58 () Included in other current assets and other property and investments on the balance sheet. See Note (K) under "Southern Power" for additional information on the Garland battery energy storage facility.

Consolidated Entities and Equit

Consolidated Entities and Equity Method Investments	9 Months Ended
Consolidated Entities and Equity Method Investments	Sep. 30, 2021
Regulated Operations [Abstract]
Consolidated Entities and Equity Method Investments	CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTSSee Note 7 to the financial statements in Item 8 of the Form 10-K for additional information. Southern Power Variable Interest Entities Southern Power has certain subsidiaries that are determined to be VIEs. Southern Power is considered the primary beneficiary of these VIEs because it controls the most significant activities of the VIEs, including operating and maintaining the respective assets, and has the obligation to absorb expected losses of these VIEs to the extent of its equity interests. SP Solar and SP Wind At September 30, 2021 and December 31, 2020, SP Solar had total assets of $6.2 billion and $6.1 billion, respectively, total liabilities of $364 million and $387 million, respectively, and noncontrolling interests of $1.1 billion. Cash distributions from SP Solar are allocated 67% to Southern Power and 33% to Global Atlantic in accordance with their partnership interest percentage. Under the terms of the limited partnership agreement, distributions without limited partner consent are limited to available cash and SP Solar is obligated to distribute all such available cash to its partners each quarter. Available cash includes all cash generated in the quarter subject to the maintenance of appropriate operating reserves. At September 30, 2021 and December 31, 2020, SP Wind had total assets of $2.3 billion and $2.4 billion, respectively, total liabilities of $157 million and $138 million, respectively, and noncontrolling interests of $42 million and $43 million, respectively. Under the terms of the limited liability agreement, distributions without Class A member consent are limited to available cash and SP Wind is obligated to distribute all such available cash to its members each quarter. Available cash includes all cash generated in the quarter subject to the maintenance of appropriate operating reserves. Cash distributions from SP Wind are generally allocated 60% to Southern Power and 40% to the three financial investors in accordance with the limited liability agreement. Southern Power consolidates both SP Solar and SP Wind, as the primary beneficiary, since it controls the most significant activities of each entity, including operating and maintaining their assets. Certain transfers and sales of the assets in the VIEs are subject to partner consent and the liabilities are non-recourse to the general credit of Southern Power. Liabilities consist of customary working capital items and do not include any long-term debt. Other Variable Interest Entities Southern Power has other consolidated VIEs that relate to certain subsidiaries that have either sold noncontrolling interests to tax-equity investors or acquired less than a 100% interest from facility developers. These entities are considered VIEs because the arrangements are structured similar to a limited partnership and the noncontrolling members do not have substantive kick-out rights. At September 30, 2021 and December 31, 2020, the other VIEs had total assets of $1.9 billion and $1.1 billion, respectively, total liabilities of $263 million and $110 million, respectively, and noncontrolling interests of $902 million and $454 million, respectively. Under the terms of the partnership agreements, distributions of all available cash are required each month or quarter and additional distributions require partner consent. Equity Method Investments At September 30, 2021 and December 31, 2020, Southern Power had equity method investments in wind and battery energy storage projects totaling $83 million and $19 million, respectively. Earnings (loss) from these investments were immaterial for all periods presented. Southern Company Gas Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments at September 30, 2021 and December 31, 2020 and related earnings (loss) from those investments for the three and nine months ended September 30, 2021 and 2020 were as follows: Investment Balance September 30, 2021 December 31, 2020 (in millions) SNG $ 1,130 $ 1,167 PennEast Pipeline () 11 91 Other 33 32 Total $ 1,174 $ 1,290 () Investment balance at September 30, 2021 reflects pre-tax impairment charges totaling $84 million recorded during 2021. See Note (C) under "Other Matters – Southern Company Gas" for additional information, including the September 2021 cancellation of the project. Three Months Ended September 30, Nine Months Ended September 30, Earnings (Loss) from Equity Method Investments 2021 2020 2021 2020 (in millions) SNG $ 27 $ 30 $ 93 $ 95 PennEast Pipeline (a)(b) (2) 2 (81) 5 Other (a)(c) — 1 2 6 Total $ 25 $ 33 $ 14 $ 106 (a) Earnings primarily result from AFUDC equity recorded by the project entity. (b) Includes pre-tax impairment charges totaling $2 million and $84 million for the three and nine months ended September 30, 2021, respectively. See Note (C) under "Other Matters – Southern Company Gas" for additional information, including the September 2021 cancellation of the project. (c) On March 24, 2020, Southern Company Gas completed the sale of its interests in Atlantic Coast Pipeline and Pivotal LNG. See Note 15 to the financial statements under "Southern Company Gas" in Item 8 of the Form 10-K for additional information.

Financing

Financing	9 Months Ended
Financing	Sep. 30, 2021
Debt Disclosure [Abstract]
Financing	FINANCING Bank Credit Arrangements See Note 8 to the financial statements under "Bank Credit Arrangements" in Item 8 of the Form 10-K for additional information. At September 30, 2021, committed credit arrangements with banks were as follows: Expires Company 2022 2023 2024 2026 Total Unused Due within One Year (in millions) Southern Company parent $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — Alabama Power — — 550 700 1,250 1,250 — Georgia Power — — — 1,750 1,750 1,726 — Mississippi Power — 125 150 — 275 250 — Southern Power (a) — — — 600 600 568 — Southern Company Gas (b) 250 — — 1,500 1,750 1,747 250 SEGCO 30 — — — 30 30 30 Southern Company $ 280 $ 125 $ 700 $ 6,550 $ 7,655 $ 7,570 $ 280 (a) Does not include Southern Power Company's $75 million and $60 million continuing letter of credit facilities for standby letters of credit expiring in 2023, of which $23 million and $1 million, respectively, was unused at September 30, 2021. Southern Power's subsidiaries are not parties to its bank credit arrangements or letter of credit facilities. (b) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $800 million of the arrangement expiring in 2026 and all $250 million of the arrangement expiring in 2022. Southern Company Gas' committed credit arrangement expiring in 2026 also includes $700 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas. Pursuant to the multi-year credit arrangement expiring in 2026, the allocations between Southern Company Gas Capital and Nicor Gas may be adjusted. As reflected in the table above, in May 2021, Southern Company, Alabama Power, Georgia Power, and Southern Power each amended and restated certain of its multi-year credit arrangements, which, among other things, extended the maturity dates from 2024 to 2026. Alabama Power also decreased the borrowing capacity under its credit arrangement now maturing in 2026 from $800 million to $700 million. Also in May 2021, Southern Company Gas Capital, along with Nicor Gas, amended and restated their multi-year credit arrangement to extend the maturity date from 2024 to 2026 and decrease the aggregate borrowing capacity from $1.75 billion to $1.5 billion. In addition, Southern Company Gas Capital entered into a new $250 million credit arrangement, which is guaranteed by Southern Company Gas, that matures in 2022. In June 2021, Mississippi Power amended and restated certain of its multi-year credit arrangements aggregating $150 million, which, among other things, extended the maturity dates from 2022 to 2024. In August 2021, Alabama Power amended and restated one of its multi-year credit arrangements, which, among other things, extended the maturity date from 2022 to 2024 and increased the borrowing capacity from $525 million to $550 million. Subject to applicable market conditions, Southern Company and its subsidiaries expect to renew or replace their bank credit arrangements as needed, prior to expiration. In connection therewith, Southern Company and its subsidiaries may extend the maturity dates and/or increase or decrease the lending commitments thereunder. These bank credit arrangements, as well as the term loan arrangements of the Registrants, Nicor Gas, and SEGCO, contain covenants that limit debt levels and contain cross-acceleration or, in the case of Southern Power, cross-default provisions to other indebtedness (including guarantee obligations) that are restricted only to the indebtedness of the individual company. Such cross-default provisions to other indebtedness would trigger an event of default if Southern Power defaulted on indebtedness or guarantee obligations over a specified threshold. Such cross-acceleration provisions to other indebtedness would trigger an event of default if the applicable borrower defaulted on indebtedness, the payment of which was then accelerated. At September 30, 2021, the Registrants, Nicor Gas, and SEGCO were in compliance with all such covenants. None of the bank credit arrangements contain material adverse change clauses at the time of borrowings. A portion of the unused credit with banks is allocated to provide liquidity support to the revenue bonds of the traditional electric operating companies and the commercial paper programs of the Registrants, Nicor Gas, and SEGCO. The amount of variable rate revenue bonds of the traditional electric operating companies outstanding requiring liquidity support at September 30, 2021 was approximately $1.6 billion (comprised of approximately $854 million at Alabama Power, $672 million at Georgia Power, and $34 million at Mississippi Power). In addition, at September 30, 2021, Georgia Power and Mississippi Power had approximately $262 million and $50 million, respectively, of fixed rate revenue bonds outstanding that are required to be remarketed within the next 12 months. Earnings per Share For Southern Company, the only differences in computing basic and diluted earnings per share are attributable to awards outstanding under stock-based compensation plans and the equity units issued in 2019. Earnings per share dilution resulting from stock-based compensation plans and the equity units issuance is determined using the treasury stock method. See Note 8 to the financial statements under "Equity Units" in Item 8 of the Form 10-K for information on the equity units and Note 12 to the financial statements in Item 8 of the Form 10-K for information on stock-based compensation plans. Shares used to compute diluted earnings per share were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in millions) As reported shares 1,061 1,058 1,060 1,058 Effect of stock-based compensation 7 6 7 6 Diluted shares 1,068 1,064 1,067 1,064 For all periods presented, an immaterial number of stock-based compensation awards was not included in the diluted earnings per share calculation because the awards were anti-dilutive. An immaterial number of shares related to the equity units issued in 2019 was included in the calculations of diluted earnings per share for the nine months ended September 30, 2020. There were no such amounts for all other periods presented.

Income Taxes

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES See Note 10 to the financial statements in Item 8 of the Form 10-K for additional tax information. Current and Deferred Income Taxes Tax Credit and Net Operating Loss Carryforwards Southern Company had federal ITC and PTC carryforwards (primarily related to Southern Power) totaling $1.2 billion at September 30, 2021 compared to $1.4 billion at December 31, 2020. The federal ITC and PTC carryforwards begin expiring in 2036 and 2032, respectively, but are expected to be fully utilized by 2024. The utilization of each Registrant's estimated tax credit and state net operating loss carryforwards and related valuation allowances could be impacted by numerous factors, including the acquisition of additional renewable projects, the purchase of rights to additional PTCs of Plant Vogtle Units 3 and 4 pursuant to certain joint ownership agreements, changes in taxable income projections, and potential income tax rate changes. See Note (B) and Note 2 to the financial statements in Item 8 of the Form 10-K under "Georgia Power – Nuclear Construction" for additional information on Plant Vogtle Units 3 and 4. Valuation Allowances Details of significant changes in valuation allowances for the applicable Registrants are provided below: Southern Company Georgia Power (in millions) Federal $ 20 $ — State (net of federal benefit) 92 28 Balance at December 31, 2020 $ 112 $ 28 Federal $ 20 $ — State (net of federal benefit) 122 58 Balance at September 30, 2021 $ 142 $ 58 The increase in valuation allowances, net of federal benefit, for Southern Company and Georgia Power during 2021 was primarily due to Georgia Power's projected inability to utilize certain state tax credit carryforwards. Effective Tax Rate Details of significant changes in the effective tax rate for the applicable Registrants are provided herein. Southern Company Southern Company's effective tax rate is typically lower than the statutory rate due to employee stock plans' dividend deduction, non-taxable AFUDC equity at the traditional electric operating companies, flowback of excess deferred income taxes at the regulated utilities, and federal income tax benefits from ITCs and PTCs primarily at Southern Power. Southern Company's effective tax rate was 17.5% for the nine months ended September 30, 2021 compared to 13.9% for the corresponding period in 2020. The effective tax rate increase was primarily related to changes in state apportionment rates as a result of the sale of Sequent, an increase in the valuation allowance on certain state tax credit carryforwards, and the tax impact of the second quarter 2020 charge to earnings associated with a leveraged lease investment. See "Valuation Allowances" herein, Note (K) under "Southern Company Gas," and Note 3 to the financial statements in Item 8 of the Form 10-K under "Other Matters – Southern Company" for additional information. Georgia Power Georgia Power's effective tax rate was 7.3% for the nine months ended September 30, 2021 compared to 12.3% for the corresponding period in 2020. The effective tax rate decrease was primarily due to higher charges to earnings in 2021 associated with the construction of Plant Vogtle Units 3 and 4, partially offset by an increase in the valuation allowance on certain state tax credit carryforwards. See "Valuation Allowances" herein and Note (B) under "Georgia Power – Nuclear Construction" for additional information. Southern Power Southern Power's effective tax benefit rate was (1.6)% for the nine months ended September 30, 2021 compared to an effective tax rate of 11.3% for the corresponding period in 2020. The effective tax rate decrease was primarily due to changes in state apportionment methodology resulting from tax legislation enacted by the State of Alabama in February 2021, as well as the tax impact from the sale of Plant Mankato in January 2020. See Note 15 to the financial statements under "Southern Power" in Item 8 of the Form 10-K for additional information.

Retirement Benefits

Retirement Benefits	9 Months Ended
Retirement Benefits	Sep. 30, 2021
Retirement Benefits [Abstract]
Retirement Benefits	RETIREMENT BENEFITS The Southern Company system has a qualified defined benefit, trusteed, pension plan covering substantially all employees, with the exception of employees at PowerSecure. The qualified pension plan is funded in accordance with requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA). No mandatory contributions to the qualified pension plan are anticipated for the year ending December 31, 2021. The Southern Company system also provides certain non-qualified defined benefits for a select group of management and highly compensated employees, which are funded on a cash basis. In addition, the Southern Company system provides certain medical care and life insurance benefits for retired employees through other postretirement benefit plans. The traditional electric operating companies fund other postretirement trusts to the extent required by their respective regulatory commissions. Southern Company Gas has a separate unfunded supplemental retirement health care plan that provides medical care and life insurance benefits to employees of discontinued businesses. See Note 11 to the financial statements in Item 8 of the Form 10-K for additional information. On each Registrant's condensed statements of income, the service cost component of net periodic benefit costs is included in other operations and maintenance expenses and all other components of net periodic benefit costs are included in other income (expense), net. Components of the net periodic benefit costs for the three and nine months ended September 30, 2021 and 2020 are presented in the following tables. Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2021 Pension Plans Service cost $ 109 $ 26 $ 28 $ 4 $ 2 $ 10 Interest cost 87 20 26 4 2 6 Expected return on plan assets (298) (72) (94) (14) (4) (21) Amortization: Prior service costs — — — — — (1) Regulatory asset — — — — — 3 Net (gain)/loss 78 21 25 4 1 3 Net periodic pension cost (income) $ (24) $ (5) $ (15) $ (2) $ 1 $ — Postretirement Benefits Service cost $ 6 $ 2 $ 2 $ 1 $ 1 $ — Interest cost 9 2 3 — — 1 Expected return on plan assets (19) (8) (7) (1) — (2) Amortization: Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ (3) $ (4) $ (1) $ — $ 1 $ — Nine Months Ended September 30, 2021 Pension Plans Service cost $ 326 $ 77 $ 84 $ 13 $ 7 $ 28 Interest cost 260 61 78 12 4 18 Expected return on plan assets (893) (215) (282) (41) (11) (64) Amortization: Prior service costs — — 1 — — (2) Regulatory asset — — — — — 11 Net (gain)/loss 235 62 75 11 3 9 Net periodic pension cost (income) $ (72) $ (15) $ (44) $ (5) $ 3 $ — Postretirement Benefits Service cost $ 18 $ 5 $ 5 $ 1 $ 1 $ 1 Interest cost 26 6 9 1 — 3 Expected return on plan assets (57) (22) (20) (2) — (6) Amortization: Prior service costs (1) — — — — — Regulatory asset — — — — — 5 Net (gain)/loss 3 — 2 — — (2) Net periodic postretirement benefit cost (income) $ (11) $ (11) $ (4) $ — $ 1 $ 1 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2020 Pension Plans Service cost $ 94 $ 23 $ 24 $ 3 $ 2 $ 8 Interest cost 108 25 33 5 1 8 Expected return on plan assets (274) (66) (87) (13) (4) (20) Amortization: Prior service costs — 1 — — — (1) Regulatory asset — — — — — 4 Net (gain)/loss 67 17 22 4 1 2 Net periodic pension cost (income) $ (5) $ — $ (8) $ (1) $ — $ 1 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ (1) $ 1 $ — Interest cost 13 4 5 1 — 2 Expected return on plan assets (18) (7) (7) — — (2) Amortization: Prior service costs — — (1) — — — Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ 2 $ (2) $ — $ — $ 1 $ 1 Nine Months Ended September 30, 2020 Pension Plans Service cost $ 282 $ 67 $ 72 $ 11 $ 6 $ 24 Interest cost 324 75 100 15 4 23 Expected return on plan assets (824) (198) (261) (38) (10) (59) Amortization: Prior service costs 1 1 1 — — (2) Regulatory asset — — — — — 12 Net (gain)/loss 201 53 65 10 2 7 Net periodic pension cost (income) $ (16) $ (2) $ (23) $ (2) $ 2 $ 5 Postretirement Benefits Service cost $ 17 $ 4 $ 5 $ — $ 1 $ 1 Interest cost 40 10 15 2 — 5 Expected return on plan assets (54) (21) (20) (1) — (5) Amortization: Prior service costs (1) — (1) — — — Regulatory asset — — — — — 5 Net (gain)/loss 2 — 2 — — (2) Net periodic postretirement benefit cost (income) $ 4 $ (7) $ 1 $ 1 $ 1 $ 4

Fair Value Measurements

Fair Value Measurements	9 Months Ended
Fair Value Measurements	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS At September 30, 2021, assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using: At September 30, 2021 Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 75 $ 425 $ — $ — $ 500 Interest rate derivatives — 25 — — 25 Foreign currency derivatives — 20 — — 20 Investments in trusts: (b)(c) Domestic equity 738 237 — — 975 Foreign equity 167 183 — — 350 U.S. Treasury and government agency securities — 352 — — 352 Municipal bonds — 48 — — 48 Pooled funds – fixed income — 14 — — 14 Corporate bonds 2 472 — — 474 Mortgage and asset backed securities — 92 — — 92 Private equity — — — 123 123 Cash and cash equivalents 5 — — — 5 Other 29 13 — — 42 Cash equivalents 1,498 9 — — 1,507 Other investments 9 26 — — 35 Total $ 2,523 $ 1,916 $ — $ 123 $ 4,562 Liabilities: Energy-related derivatives (a) $ 27 $ 17 $ — $ — $ 44 Interest rate derivatives — 16 — — 16 Foreign currency derivatives — 43 — — 43 Contingent consideration — — 16 — 16 Other — 13 — — 13 Total $ 27 $ 89 $ 16 $ — $ 132 Fair Value Measurements Using: At September 30, 2021 Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 104 $ — $ — $ 104 Interest rate derivatives — 5 — — 5 Nuclear decommissioning trusts: (b) Domestic equity 444 227 — — 671 Foreign equity 167 — — — 167 U.S. Treasury and government agency securities — 22 — — 22 Municipal bonds — 1 — — 1 Corporate bonds 2 243 — — 245 Mortgage and asset backed securities — 22 — — 22 Private equity — — — 123 123 Other 6 — — — 6 Cash equivalents 443 9 — — 452 Other investments — 26 — — 26 Total $ 1,062 $ 659 $ — $ 123 $ 1,844 Liabilities: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Georgia Power Assets: Energy-related derivatives $ — $ 166 $ — $ — $ 166 Nuclear decommissioning trusts: (b)(c) Domestic equity 294 1 — — 295 Foreign equity — 180 — — 180 U.S. Treasury and government agency securities — 330 — — 330 Municipal bonds — 47 — — 47 Corporate bonds — 229 — — 229 Mortgage and asset backed securities — 70 — — 70 Other 23 13 — — 36 Cash equivalents 240 — — — 240 Total $ 557 $ 1,036 $ — $ — $ 1,593 Liabilities: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Fair Value Measurements Using: At September 30, 2021 Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 105 $ — $ — $ 105 Cash equivalents 121 — — — 121 Total $ 121 $ 105 $ — $ — $ 226 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Southern Power Assets: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Foreign currency derivatives — 20 — — 20 Total $ — $ 30 $ — $ — $ 30 Liabilities: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Foreign currency derivatives — 11 — — 11 Contingent consideration — — 16 — 16 Other — 13 — — 13 Total $ — $ 26 $ 16 $ — $ 42 Southern Company Gas Assets: Energy-related derivatives (a) $ 75 $ 40 $ — $ — $ 115 Interest rate derivatives — 6 — — 6 Non-qualified deferred compensation trusts: Domestic equity — 9 — — 9 Foreign equity — 3 — — 3 Pooled funds – fixed income — 14 — — 14 Cash equivalents 5 — — — 5 Total $ 80 $ 72 $ — $ — $ 152 Liabilities: Energy-related derivatives (a) $ 27 $ 4 $ — $ — $ 31 Interest rate derivatives — 4 — — 4 Total $ 27 $ 8 $ — $ — $ 35 (a) Excludes cash collateral of $(20) million. (b) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. (c) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. At September 30, 2021, approximately $57 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. See Note (K) under "Assets Held for Sale" for information regarding assets recorded at fair value on a nonrecurring basis. Southern Company, Alabama Power, and Georgia Power continue to elect the option to fair value investment securities held in the nuclear decommissioning trust funds. The fair value of the funds, including reinvested interest and dividends and excluding the funds' expenses, increased (decreased) by the amounts shown in the table below for the nine months ended September 30, 2021 and 2020. The changes were recorded as a change to the regulatory assets and liabilities related to AROs for Georgia Power and Alabama Power, respectively. Fair value increases (decreases) Three Months Ended September 30, 2021 Three Months Ended September 30, 2020 Nine Months Ended September 30, 2021 Nine Months Ended September 30, 2020 (in millions) Southern Company $ 9 $ 108 $ 173 $ 85 Alabama Power 15 66 133 24 Georgia Power (6) 42 40 61 Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and over-the-counter financial products for natural gas and physical power products, including, from time to time, basis swaps. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices, power prices, implied volatility, and overnight index swap interest rates. Interest rate derivatives are also standard over-the-counter products that are valued using observable market data and assumptions commonly used by market participants. The fair value of interest rate derivatives reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and occasionally, implied volatility of interest rate options. The fair value of cross-currency swaps reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future foreign currency exchange rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and discount rates. The interest rate derivatives and cross-currency swaps are categorized as Level 2 under Fair Value Measurements as these inputs are based on observable data and valuations of similar instruments. See Note (J) for additional information on how these derivatives are used. For fair value measurements of the investments within the nuclear decommissioning trusts and the non-qualified deferred compensation trusts, external pricing vendors are designated for each asset class with each security specifically assigned a primary pricing source. For investments held within commingled funds, fair value is determined at the end of each business day through the net asset value, which is established by obtaining the underlying securities' individual prices from the primary pricing source. A market price secured from the primary source vendor is then evaluated by management in its valuation of the assets within the trusts. As a general approach, fixed income market pricing vendors gather market data (including indices and market research reports) and integrate relative credit information, observed market movements, and sector news into proprietary pricing models, pricing systems, and mathematical tools. Dealer quotes and other market information, including live trading levels and pricing analysts' judgments, are also obtained when available. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. See Note 6 to the financial statements under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information. Southern Power has contingent payment obligations related to certain acquisitions whereby it is primarily obligated to make generation-based payments to the seller, which commenced at the commercial operation of the respective facility and continue through 2026. The obligations are categorized as Level 3 under Fair Value Measurements as the fair value is determined using significant unobservable inputs for the forecasted facility generation in MW-hours, as well as other inputs such as a fixed dollar amount per MW-hour, and a discount rate. The fair value of contingent consideration reflects the net present value of expected payments and any periodic change arising from forecasted generation is expected to be immaterial. Southern Power also has payment obligations through 2040 whereby it must reimburse the transmission owners for interconnection facilities and network upgrades constructed to support connection of a Southern Power generating facility to the transmission system. The obligations are categorized as Level 2 under Fair Value Measurements as the fair value is determined using observable inputs for the contracted amounts and reimbursement period, as well as a discount rate. The fair value of the obligations reflects the net present value of expected payments. "Other investments" include investments traded in the open market that have maturities greater than 90 days, which are categorized as Level 2 under Fair Value Measurements and are comprised of corporate bonds, bank certificates of deposit, treasury bonds, and/or agency bonds. At September 30, 2021, the fair value measurements of private equity investments held in Alabama Power's nuclear decommissioning trusts that are calculated at net asset value per share (or its equivalent) as a practical expedient totaled $123 million and unfunded commitments related to the private equity investments totaled $72 million. Private equity investments include high-quality private equity funds across several market sectors and funds that invest in real estate assets. Private equity funds do not have redemption rights. Distributions from these funds will be received as the underlying investments in the funds are liquidated. At September 30, 2021, other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas () (in billions) Long-term debt, including securities due within one year: Carrying amount $ 51.9 $ 9.1 $ 13.6 $ 1.6 $ 4.0 $ 6.8 Fair value 57.6 10.4 15.2 1.7 4.4 7.8 () The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the 2016 merger with Southern Company. Southern Company Gas amortizes the fair value adjustments over the remaining lives of the respective bonds, the latest being through 2043. The fair values are determined using Level 2 measurements and are based on quoted market prices for the same or similar issues or on the current rates available to the Registrants. Commodity Contracts with Level 3 Valuation Inputs Prior to July 1, 2021, Southern Company Gas had Level 3 physical natural gas forward contracts related to Sequent. See Note (K) under "Southern Company Gas" for information regarding the sale of Sequent. Since commodity contracts classified as Level 3 typically include a combination of observable and unobservable components, the changes in fair value may include amounts due in part to observable market factors, or changes to assumptions on the unobservable components. The following table provides a reconciliation of Southern Company Gas' Level 3 contracts during the three and nine months ended September 30, 2021. Three Months Ended September 30, 2021 Nine Months Ended September 30, 2021 (in millions) Beginning balance $ 18 $ 28 Instruments realized or otherwise settled during period — (6) Changes in fair value — (4) Sale of Sequent (18) (18) Ending balance $ — $ — Changes in fair value of Level 3 instruments represent changes in gains and losses for the periods that are reported on Southern Company Gas' statements of income in natural gas revenues prior to the sale of Sequent.

Derivatives

Derivatives	9 Months Ended
Derivatives	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	DERIVATIVES Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to market risks, including commodity price risk, interest rate risk, weather risk, and occasionally foreign currency exchange rate risk. To manage the volatility attributable to these exposures, each company nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to each company's policies in areas such as counterparty exposure and risk management practices. Through the sale of Sequent on July 1, 2021, Southern Company Gas' wholesale gas operations used various contracts in its commercial activities that generally met the definition of derivatives. For the traditional electric operating companies, Southern Power, and Southern Company Gas' other businesses, each company's policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note (I) for additional fair value information. In the statements of cash flows, any cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. Any cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with the classification of the hedged interest or principal, respectively. See Note 1 to the financial statements under "Financial Instruments" in Item 8 of the Form 10-K for additional information. See Note (K) under "Southern Company Gas" for information regarding Southern Company Gas' sale of Sequent. Energy-Related Derivatives The traditional electric operating companies, Southern Power, and Southern Company Gas enter into energy-related derivatives to hedge exposures to electricity, natural gas, and other fuel price changes. However, due to cost-based rate regulations and other various cost recovery mechanisms, the traditional electric operating companies and the natural gas distribution utilities have limited exposure to market volatility in energy-related commodity prices. Each of the traditional electric operating companies and certain of the natural gas distribution utilities of Southern Company Gas manage fuel-hedging programs, implemented per the guidelines of their respective state PSCs or other applicable state regulatory agencies, through the use of financial derivative contracts, which are expected to continue to mitigate price volatility. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non-exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in operating revenues. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges – Energy-related derivative contracts designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through an approved cost recovery mechanism. • Cash Flow Hedges – Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in accumulated OCI before being recognized in the statements of income in the same period and in the same income statement line item as the earnings effect of the hedged transactions. • Not Designated – Gains and losses on energy-related derivative contracts that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Some energy-related derivative contracts require physical delivery as opposed to financial settlement, and this type of derivative is both common and prevalent within the electric and natural gas industries. When an energy-related derivative contract is settled physically, any cumulative unrealized gain or loss is reversed and the contract price is recognized in the respective line item representing the actual price of the underlying goods being delivered. At September 30, 2021, the net volume of energy-related derivative contracts for natural gas positions, together with the longest hedge date over which the respective entity is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Net Longest Longest (in millions) Southern Company () 336 2030 2024 Alabama Power 75 2024 — Georgia Power 99 2024 — Mississippi Power 79 2025 — Southern Power 6 2030 2022 Southern Company Gas () 77 2024 2024 () Southern Company Gas' derivative instruments include both long and short natural gas positions. A long position is a contract to purchase natural gas and a short position is a contract to sell natural gas. Southern Company Gas' volume represents the net of long natural gas positions of 91.4 million mmBtu and short natural gas positions of 14.3 million mmBtu at September 30, 2021, which is also included in Southern Company's total volume. See Note (K) under "Southern Company Gas" for information regarding Southern Company Gas' sale of Sequent. In addition to the volumes discussed above, the traditional electric operating companies and Southern Power enter into physical natural gas supply contracts that provide the option to sell back excess natural gas due to operational constraints. The maximum expected volume of natural gas subject to such a feature is 41 million mmBtu for Southern Company, which includes 10 million mmBtu for Alabama Power, 13 million mmBtu for Georgia Power, 5 million mmBtu for Mississippi Power, and 13 million mmBtu for Southern Power. For cash flow hedges of energy-related derivatives, the estimated pre-tax gains (losses) expected to be reclassified from accumulated OCI to earnings for the 12-month period ending September 30, 2022 are immaterial for all Registrants. Interest Rate Derivatives Southern Company and certain subsidiaries may enter into interest rate derivatives to hedge exposure to changes in interest rates. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and presented on the same income statement line item as the earnings effect of the hedged transactions. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings on the same income statement line item. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. At September 30, 2021, the following interest rate derivatives were outstanding: Notional Interest Weighted Hedge Fair Value Gain (Loss) at September 30, 2021 (in millions) (in millions) Cash Flow Hedges of Forecasted Debt Alabama Power $ 150 — 1.91% August 2051 $ 5 Fair Value Hedges of Existing Debt Southern Company parent 400 1.75% 1-month LIBOR + 0.68% March 2028 (2) Southern Company parent 1,000 3.70% 1-month LIBOR + 2.36% April 3 Southern Company Gas 500 1.75% 1-month LIBOR + 0.38% January 2031 2 Southern Company $ 2,050 $ 8 For cash flow hedge interest rate derivatives, the estimated pre-tax gains (losses) expected to be reclassified from accumulated OCI to interest expense for the 12-month period ending September 30, 2022 total $(22) million for Southern Company and are immaterial for all other Registrants. Deferred gains and losses related to interest rate derivatives are expected to be amortized into earnings through 2051 for the Southern Company parent entity, 2051 for Alabama Power, 2044 for Georgia Power, 2028 for Mississippi Power, and 2046 for Southern Company Gas. Foreign Currency Derivatives Southern Company and certain subsidiaries, including Southern Power, may enter into foreign currency derivatives to hedge exposure to changes in foreign currency exchange rates, such as that arising from the issuance of debt denominated in a currency other than U.S. dollars. Derivatives related to forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and on the same income statement line as the earnings effect of the hedged transactions, including foreign currency gains or losses arising from changes in the U.S. currency exchange rates. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings on the same income statement line item, including foreign currency gains or losses arising from changes in the U.S. currency exchange rates. Southern Company has elected to exclude the cross-currency basis spread from the assessment of effectiveness in the fair value hedges of its foreign currency risk and record any difference between the change in the fair value of the excluded components and the amounts recognized in earnings as a component of OCI. At September 30, 2021, the following foreign currency derivatives were outstanding: Pay Notional Pay Receive Notional Receive Hedge Fair Value Gain (Loss) at September 30, 2021 (in millions) (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company parent $ 1,476 3.39% € 1,250 1.88% September 2027 $ (32) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 9 Southern Power 564 3.78% 500 1.85% June 2026 — Southern Power total $ 1,241 € 1,100 $ 9 Southern Company $ 2,717 € 2,350 $ (23) The estimated pre-tax gain (loss) related to Southern Power's foreign currency derivatives accounted for as cash flow hedges expected to be reclassified from accumulated OCI to earnings for the 12-month period ending September 30, 2022 is $(4) million. Derivative Financial Statement Presentation and Amounts Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas enter into derivative contracts that may contain certain provisions that permit intra-contract netting of derivative receivables and payables for routine billing and offsets related to events of default and settlements. Southern Company and certain subsidiaries also utilize master netting agreements to mitigate exposure to counterparty credit risk. These agreements may contain provisions that permit netting across product lines and against cash collateral. The fair value amounts of derivative assets and liabilities on the balance sheet are presented net to the extent that there are netting arrangements or similar agreements with the counterparties. The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 308 $ 9 $ 24 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 118 6 18 19 Total derivatives designated as hedging instruments for regulatory purposes $ 426 $ 15 $ 42 $ 30 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 41 $ — $ 3 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 4 — — — Interest rate derivatives: Assets from risk management activities/Other current liabilities 25 — 20 — Other deferred charges and assets/Other deferred credits and liabilities — 16 — — Foreign currency derivatives: Assets from risk management activities/Other current liabilities 9 33 — 23 Other deferred charges and assets/Other deferred credits and liabilities 11 10 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 90 $ 59 $ 110 $ 28 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 29 $ 29 $ 388 $ 331 Other deferred charges and assets/Other deferred credits and liabilities 1 — 270 232 Total derivatives not designated as hedging instruments $ 30 $ 29 $ 658 $ 563 Gross amounts recognized $ 546 $ 103 $ 810 $ 621 Gross amounts offset (a) (57) (37) (529) (557) Net amounts recognized in the Balance Sheets (b) $ 489 $ 66 $ 281 $ 64 At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 67 $ 2 $ 7 $ 2 Other deferred charges and assets/Other deferred credits and liabilities 37 2 5 5 Total derivatives designated as hedging instruments for regulatory purposes $ 104 $ 4 $ 12 $ 7 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ 5 $ — $ — $ — Gross amounts recognized $ 109 $ 4 $ 12 $ 7 Gross amounts offset (3) (3) (7) (7) Net amounts recognized in the Balance Sheets $ 106 $ 1 $ 5 $ — Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 124 $ 2 $ 7 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 42 2 8 8 Total derivatives designated as hedging instruments for regulatory purposes $ 166 $ 4 $ 15 $ 13 Gross amounts recognized $ 166 $ 4 $ 15 $ 13 Gross amounts offset (3) (3) (12) (12) Net amounts recognized in the Balance Sheets $ 163 $ 1 $ 3 $ 1 Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 66 $ 1 $ 4 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 39 2 5 6 Total derivatives designated as hedging instruments for regulatory purposes $ 105 $ 3 $ 9 $ 9 Gross amounts recognized $ 105 $ 3 $ 9 $ 9 Gross amounts offset (2) (2) (7) (7) Net amounts recognized in the Balance Sheets $ 103 $ 1 $ 2 $ 2 At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 8 $ — $ 2 $ 2 Other deferred charges and assets/Other deferred credits and liabilities 1 — — — Foreign currency derivatives: Other current assets/Other current liabilities 9 11 — 23 Other deferred charges and assets/Other deferred credits and liabilities 11 — 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 29 $ 11 $ 89 $ 25 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 2 $ — $ 1 Total derivatives not designated as hedging instruments $ 1 $ 2 $ — $ 1 Gross amounts recognized $ 30 $ 13 $ 89 $ 26 Gross amounts offset (1) (1) — — Net amounts recognized in the Balance Sheets $ 29 $ 12 $ 89 $ 26 At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 51 $ 4 $ 6 $ 1 Total derivatives designated as hedging instruments for regulatory purposes $ 51 $ 4 $ 6 $ 1 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 33 $ — $ 1 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 3 — — — Interest rate derivatives: Assets from risk management activities/Liabilities from risk management activities-current 6 — — — Other deferred charges and assets/Other deferred credits and liabilities — 4 — — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 42 $ 4 $ 1 $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 28 $ 27 $ 388 $ 330 Other deferred charges and assets/Other deferred credits and liabilities 1 — 270 232 Total derivatives not designated as hedging instruments $ 29 $ 27 $ 658 $ 562 Gross amounts recognized $ 122 $ 35 $ 665 $ 566 Gross amounts offset (a) (48) (28) (503) (531) Net amounts recognized in the Balance Sheets (b) $ 74 $ 7 $ 162 $ 35 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $(20) million and $28 million at September 30, 2021 and December 31, 2020, respectively. (b) Net amounts of derivative instruments outstanding exclude immaterial premium and intrinsic value associated with weather derivatives for both periods presented. The traditional electric operating companies had no energy-related derivatives not designated as hedging instruments at September 30, 2021 or December 31, 2020. At September 30, 2021 and December 31, 2020, the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) At September 30, 2021: Energy-related derivatives: Other regulatory assets, current $ (5) $ (1) $ (1) $ — $ (3) Other regulatory liabilities, current 297 66 123 66 42 Other regulatory liabilities, deferred 112 35 40 37 — Total energy-related derivative gains (losses) $ 404 $ 100 $ 162 $ 103 $ 39 At December 31, 2020: Energy-related derivatives: Other regulatory assets, deferred $ (2) $ — $ (1) $ (1) $ — Other regulatory liabilities, current 12 5 2 1 4 Other regulatory liabilities, deferred 2 1 1 — — Total energy-related derivative gains (losses) $ 12 $ 6 $ 2 $ — $ 4 For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of cash flow and fair value hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months Ended September 30, For the Nine Months Ended September 30, 2021 2020 2021 2020 (in millions) (in millions) Southern Company Cash flow hedges: Energy-related derivatives $ 38 $ 9 $ 59 $ 2 Interest rate derivatives 5 1 7 (27) Foreign currency derivatives (36) 54 (79) (10) Fair value hedges () : Foreign currency derivatives (4) — (4) — Total $ 3 $ 64 $ (17) $ (35) Southern Power Cash flow hedges: Energy-related derivatives $ 8 $ 5 $ 16 $ 2 Foreign currency derivatives (36) 54 (79) (10) Total $ (28) $ 59 $ (63) $ (8) Southern Company Gas Cash flow hedges: Energy-related derivatives $ 30 $ 4 $ 43 $ — Interest rate derivatives — 1 — (24) Total $ 30 $ 5 $ 43 $ (24) () Represents amounts excluded from the assessment of effectiveness for which the difference between changes in fair value and periodic amortization is recorded in OCI. For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of interest rate derivatives designated as cash flow hedging instruments on accumulated OCI were immaterial for the other Registrants. For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of cash flow and fair value hedge accounting on income were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months Ended September 30, For the Nine Months Ended September 30, 2021 2020 2021 2020 (in millions) (in millions) Southern Company Total cost of natural gas $ 129 $ 71 $ 943 $ 654 Gain (loss) on energy-related cash flow hedges (a) 2 — — (8) Total depreciation and amortization 896 889 2,658 2,619 Gain (loss) on energy-related cash flow hedges (a) 3 (1) 6 (3) Total interest expense, net of amounts capitalized (451) (443) (1,352) (1,343) Gain (loss) on interest rate cash flow hedges (a) (7) (6) (20) (19) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) (18) (18) Gain (loss) on interest rate fair value hedges (b) (4) (3) (16) 27 Total other income (expense), net 131 113 297 319 Gain (loss) on foreign currency cash flow hedges (a)(c) (34) 56 (76) 52 Gain (loss) on foreign currency fair value hedges (32) — (32) — Amount excluded from effectiveness testing recognized in earnings 4 — 4 — Southern Power Total depreciation and amortization $ 132 $ 129 $ 383 $ 367 Gain (loss) on energy-related cash flow hedges (a) 3 (1) 6 (3) Total interest expense, net of amounts capitalized (36) (36) (111) (114) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) (18) (18) Total other income (expense), net 2 13 10 19 Gain (loss) on foreign currency cash flow hedges (a)(c) (34) 56 (76) 52 (a) Reclassified from accumulated OCI into earnings. (b) For fair value hedges, changes in the fair value of the derivative contracts are generally equal to changes in the fair value of the underlying debt and have no material impact on income. (c) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes. For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of cash flow and fair value hedge accounting on income for energy-related derivatives and interest rate derivatives were immaterial for the traditional electric operating companies and Southern Company Gas. At September 30, 2021 and December 31, 2020, the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items At September 30, 2021 At December 31, 2020 At September 30, 2021 At December 31, 2020 (in millions) (in millions) Southern Company Securities due within one year $ — $ (1,509) $ — $ (10) Long-term debt (3,320) — — — Southern Company Gas Long-term debt $ (497) $ — $ (1) $ — For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income of Southern Company and Southern Company Gas were as follows: Gain (Loss) Three Months Ended September 30, Nine Months Ended September 30, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2021 2020 2021 2020 (in millions) (in millions) Energy-related derivatives: Natural gas revenues () $ (2) $ (30) $ (122) $ 54 Cost of natural gas 20 5 36 18 Total derivatives in non-designated hedging relationships $ 18 $ (25) $ (86) $ 72 (*) Excludes immaterial gains (losses) recorded in natural gas revenues associated with weather derivatives for all periods presented. For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of energy-related derivatives not designated as hedging instruments were immaterial for all other Registrants. Contingent Features Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas do not have any credit arrangements that would require material changes in payment schedules or terminations as a result of a credit rating downgrade. There are certain derivatives that could require collateral, but not accelerated payment, in the event of various credit rating changes of certain Southern Company subsidiaries. At September 30, 2021, the Registrants had no collateral posted with derivative counterparties to satisfy these arrangements. At September 30, 2021, the Registrants had no interest rate derivative liabilities with contingent features. At September 30, 2021, the fair value of energy-related derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, were immaterial for all Registrants. The maximum potential collateral requirements arising from the credit-risk-related contingent features for the traditional electric operating companies and Southern Power include certain agreements that could require collateral in the event that one or more Southern Company power pool participants has a credit rating change to below investment grade. Following the sale of Gulf Power to NextEra Energy, Inc., Gulf Power is continuing to participate in the Southern Company power pool for a defined transition period that, subject to certain potential adjustments, is scheduled to end on January 1, 2024. Generally, collateral may be provided by a Southern Company guaranty, letter of credit, or cash. If collateral is required, fair value amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral are not offset against fair value amounts recognized for derivatives executed with the same counterparty. Alabama Power and Southern Power maintain accounts with certain regional transmission organizations to facilitate financial derivative transactions and they may be required to post collateral based on the value of the positions in these accounts and the associated margin requirements. At September 30, 2021, cash collateral posted in these accounts was immaterial. Southern Company Gas maintains accounts with brokers or the clearing houses of certain exchanges to facilitate financial derivative transactions. Based on the value of the positions in these accounts and the associated margin requirements, Southern Company Gas may be required to deposit cash into these accounts. At September 30, 2021, cash collateral held on deposit in broker margin accounts was $(20) million. The Registrants are exposed to losses related to financial instruments in the event of counterparties' nonperformance. The Registrants only enter into agreements and material transactions with counterparties that have investment grade credit ratings by Moody's and S&P or with counterparties who have posted collateral to cover potential credit exposure. The Registrants have also established risk management policies and controls to determine and monitor the creditworthiness of counterparties in order to mitigate their exposure to counterparty credit risk. Southern Company Gas uses established credit policies to determine and monitor the creditworthiness of counterparties, including requirements to post collateral or other credit security, as well as the quality of pledged collateral. Collateral or credit security is most often in the form of cash or letters of credit from an investment-grade financial institution, but may also include cash or U.S. government securities held by a trustee. Prior to entering a physical transaction, Southern Company Gas assigns its counterparties an internal credit rating and credit limit based on the counterparties' Moody's, S&P, and Fitch ratings, commercially available credit reports, and audited financial statements. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. Southern Company Gas utilizes netting agreements whenever possible to mitigate exposure to counterparty credit risk. Netting agreements enable Southern Company Gas to net certain assets and liabilities by counterparty across product lines and against cash collateral, provided the netting and cash collateral agreements include such provisions. While the amounts due from, or owed to, counterparties are settled net, they are recorded on a gross basis on the balance sheet as energy marketing receivables and energy marketing payables. The Registrants do not anticipate a material adverse effect on their respective financial statements as a result of counterparty nonperformance.

Acquisitions and Dispositions

Acquisitions and Dispositions	9 Months Ended
Acquisitions and Dispositions	Sep. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Acquisitions and Dispositions	ACQUISITIONS AND DISPOSITIONSSee Note 15 to the financial statements in Item 8 of the Form 10-K for additional information. Southern Company On October 29, 2021, Southern Company completed the sale of assets subject to a leveraged lease to the lessee for $45 million. No gain or loss was recognized on the sale. During the fourth quarter 2021, income tax benefits of approximately $16 million will be recognized as a result of the sale. At September 30, 2021, the leveraged lease investment was classified as held for sale. See Note 3 to the financial statements under "Other Matters – Southern Company" in Item 8 of the Form 10-K and "Assets Held for Sale" herein for additional information. Alabama Power On September 23, 2021, Alabama Power entered into an agreement to acquire all of the equity interests in Calhoun Power Company, LLC, which owns and operates the Calhoun Generating Station. See Note (B) under "Alabama Power – Calhoun Generating Station Acquisition" for additional information. Southern Power Asset Acquisition During the nine months ended September 30, 2021, Southern Power acquired a controlling membership interest in the wind facility listed below. Acquisition-related costs were expensed as incurred and were not material. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Contract Period Deuel Harvest () Wind Invenergy Renewables, LLC 300 Deuel County, SD 100% of Class B February 2021 25 years and 15 years () On March 26, 2021, Southern Power acquired a controlling interest in the project from Invenergy Renewables LLC and, on March 30, 2021, Southern Power completed a tax equity transaction whereby it sold the Class A membership interests in the project. Southern Power consolidates the project's operating results in its financial statements and the tax equity partner and Invenergy Renewables LLC each own a noncontrolling interest. Construction Projects During the nine months ended September 30, 2021, Southern Power completed construction of and placed in service 45 MWs of the Garland battery energy storage facility and continued construction of the Tranquillity battery energy storage facility, the Glass Sands wind facility, and the remainder of the Garland battery energy storage facility. Total aggregate construction costs, excluding acquisition costs, are expected to be between $400 million and $460 million for the facilities under construction. At September 30, 2021, total costs of construction incurred for these projects were $341 million, of which $228 million remains in CWIP. The ultimate outcome of these matters cannot be determined at this time. Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Projects Under Construction at September 30, 2021 Garland Solar Storage (a) Battery energy storage system 88 Kern County, CA September 2021 and fourth quarter 2021 (b) 20 years Tranquillity Solar Storage (a) Battery energy storage system 72 Fresno County, CA Fourth quarter 2021 and 20 years Glass Sands (c) Wind 118 Murray County, OK Fourth quarter 2021 12 years (a) During the third quarter 2021, Southern Power further restructured its ownership in the Garland and Tranquillity battery energy storage projects and completed tax equity transactions whereby it sold the Class A membership interests in the projects. Southern Power consolidates each project's operating results in its financial statements and the tax equity partner and two other partners each own a noncontrolling interest. (b) The facility has a total capacity of 88 MWs, of which 45 MWs were placed in service in September 2021 and 43 MWs are expected to be placed in service later in the fourth quarter 2021. (c) In December 2020, Southern Power purchased 100% of the membership interests of the Glass Sands facility. Development Projects Southern Power continues to evaluate and refine the deployment of the remaining wind turbine equipment purchased in 2016 and 2017 for development and construction projects. During the nine months ended September 30, 2021, gains on wind turbine equipment contributed to various equity method investments totaled approximately $37 million. Southern Company Gas Sale of Sequent On July 1, 2021, Southern Company Gas affiliates completed the sale of Sequent to Williams Field Services Group for a total cash purchase price of $159 million, including final working capital adjustments. The preliminary pre-tax gain associated with the transaction is approximately $121 million ($93 million after tax). As a result of the sale, changes in state apportionment rates resulted in $85 million of additional tax expense. Prior to the sale, Southern Company Gas had existing agreements in place in which it guaranteed the payment performance of Sequent. Southern Company Gas will continue to guarantee Sequent's payment performance for a period of time as Williams Field Services Group obtains releases from these obligations. At September 30, 2021, the obligations subject to the payment performance guarantee totaled $36 million. Changes in the price of natural gas, market conditions, and the number of open contracts may change the amount that Southern Company Gas is required to guarantee for Sequent each month. The maximum potential exposure over the period of the payment performance guarantee generally is capped at $1 billion. At closing, Williams Field Services Group issued a payment performance guarantee to Southern Company Gas, equal to the outstanding guarantee obligation throughout this period. Southern Company Gas' sale of Sequent did not represent a strategic shift in operations that has, or is expected to have, a major effect on its operations and financial results; therefore, none of the assets were classified as discontinued operations for any of the periods presented. Sale of Pivotal LNG In connection with its March 2020 sale of Pivotal LNG, Southern Company Gas was entitled to two $5 million payments contingent upon Dominion Modular LNG Holdings, Inc. meeting certain milestones related to Pivotal LNG. Southern Company Gas received the first payment on April 22, 2021 and expects to receive the second payment in February 2022. Assets Held for Sale The following table provides the major classes of assets classified as held for sale by Southern Company at September 30, 2021 and December 31, 2020: Southern Company At September 30, At December 31, 2021 2020 (in millions) Assets Held for Sale: Total property, plant, and equipment $ 6 $ 8 Leveraged leases 45 52 Total Assets Held for Sale $ 51 $ 60 Southern Company's assets held for sale at September 30, 2021 and December 31, 2020 were recorded at fair value on a nonrecurring basis, based primarily on unobservable inputs (Level 3). See "Southern Company" herein for additional information.

Segment and Related Information

Segment and Related Information	9 Months Ended
Segment and Related Information	Sep. 30, 2021
Segment Reporting [Abstract]
Segment and Related Information	SEGMENT AND RELATED INFORMATION Southern Company The primary businesses of the Southern Company system are electricity sales by the traditional electric operating companies and Southern Power and the distribution of natural gas by Southern Company Gas. The traditional electric operating companies – Alabama Power, Georgia Power, and Mississippi Power – are vertically integrated utilities providing electric service in three Southeastern states. Southern Power develops, constructs, acquires, owns, and manages power generation assets, including renewable energy and battery energy storage projects, and sells electricity at market-based rates in the wholesale market. Southern Company Gas distributes natural gas through its natural gas distribution utilities and is involved in several other complementary businesses including gas pipeline investments, wholesale gas services (through June 30, 2021), and gas marketing services. Southern Company's reportable business segments are the sale of electricity by the traditional electric operating companies, the sale of electricity in the competitive wholesale market by Southern Power, and the sale of natural gas and other complementary products and services by Southern Company Gas. Revenues from sales by Southern Power to the traditional electric operating companies were $167 million and $361 million for the three and nine months ended September 30, 2021, respectively, and $101 million and $279 million for the three and nine months ended September 30, 2020, respectively. Revenues from sales of natural gas from Southern Company Gas to the traditional electric operating companies were immaterial for all periods presented. Revenues from sales of natural gas from Southern Company Gas to Southern Power were $18 million for the nine months ended September 30, 2021, which represented sales from Sequent through June 30, 2021, and $9 million and $22 million for the three and nine months ended September 30, 2020, respectively. The "All Other" column includes the Southern Company parent entity, which does not allocate operating expenses to business segments. Also, this category includes segments below the quantitative threshold for separate disclosure. These segments include providing energy solutions to electric utilities and their customers in the areas of distributed generation, energy storage and renewables, and energy efficiency, as well as investments in telecommunications and leveraged lease projects. All other inter-segment revenues are not material. Financial data for business segments and products and services for the three and nine months ended September 30, 2021 and 2020 was as follows: Electric Utilities Traditional Southern Eliminations Total Southern Company Gas All Eliminations Consolidated (in millions) Three Months Ended September 30, 2021 Operating revenues $ 5,018 $ 679 $ (170) $ 5,527 $ 623 $ 124 $ (36) $ 6,238 Segment net income (loss) (a)(b)(c) 1,085 78 — 1,163 56 (121) 3 1,101 Nine Months Ended September 30, 2021 Operating revenues $ 12,813 $ 1,610 $ (372) $ 14,051 $ 2,994 $ 412 $ (111) $ 17,346 Segment net income (loss) (a)(b)(c)(d)(e)(f) 2,352 211 — 2,563 389 (338) (6) 2,608 At September 30, 2021 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Assets held for sale 3 — — 3 — 48 — 51 Total assets 89,057 13,611 (708) 101,960 22,958 3,704 (761) 127,861 Three Months Ended September 30, 2020 Operating revenues $ 4,629 $ 523 $ (103) $ 5,049 $ 477 $ 132 $ (38) $ 5,620 Segment net income (loss) (a) 1,284 74 — 1,358 14 (122) 1 1,251 Nine Months Ended September 30, 2020 Operating revenues $ 11,576 $ 1,337 $ (285) $ 12,628 $ 2,362 $ 380 $ (112) $ 15,258 Segment net income (loss) (a)(c)(f)(g) 2,571 212 — 2,783 360 (420) 9 2,732 At December 31, 2020 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Assets held for sale 5 — — 5 — 55 — 60 Total assets 85,486 13,235 (680) 98,041 22,630 3,168 (904) 122,935 (a) Attributable to Southern Company. (b) For Southern Company Gas, includes a preliminary pre-tax gain of $121 million ($93 million after tax) related to its sale of Sequent, as well as the resulting $85 million of additional tax expense due to changes in state apportionment rates. See Note (K) under "Southern Company Gas" for additional information. (c) For the traditional electric operating companies, includes pre-tax charges at Georgia Power for estimated losses associated with the construction of Plant Vogtle Units 3 and 4 of $264 million ($197 million after tax) and $772 million ($576 million after tax) for the three and nine months ended September 30, 2021, respectively, and $149 million ($111 million after tax) for the nine months ended September 30, 2020. See Note (B) and Note 2 to the financial statements in Item 8 of the Form 10-K under "Georgia Power – Nuclear Construction" for additional information. (d) For Southern Power, includes gains on wind turbine equipment contributed to various equity method investments totaling approximately $37 million pre-tax ($28 million after tax). See Notes (E) and (K) under "Southern Power" for additional information. (e) For Southern Company Gas, includes pre-tax impairment charges totaling $84 million ($67 million after tax) related to its equity method investment in the PennEast Pipeline project. See Notes (C) and (E) under "Other Matters – Southern Company Gas" and "Southern Company Gas," respectively, for additional information. (f) For the "All Other" column, includes pre-tax impairment charges related to leveraged lease investments of $7 million ($6 million after tax) and $154 million ($74 million after tax) for the nine months ended September 30, 2021 and 2020, respectively. See Note 3 to the financial statements in Item 8 of the Form 10-K under "Other Matters – Southern Company" for additional information. (g) For Southern Power, includes a $39 million pre-tax gain ($23 million gain after tax) on the sale of Plant Mankato. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Power" for additional information. Products and Services Electric Utilities' Revenues Retail Wholesale Other Total (in millions) Three Months Ended September 30, 2021 $ 4,551 $ 731 $ 245 $ 5,527 Three Months Ended September 30, 2020 4,243 584 222 5,049 Nine Months Ended September 30, 2021 $ 11,492 $ 1,822 $ 737 $ 14,051 Nine Months Ended September 30, 2020 10,503 1,473 652 12,628 Southern Company Gas' Revenues Gas Wholesale Gas Services (*) Gas Other Total (in millions) Three Months Ended September 30, 2021 $ 553 $ — $ 52 $ 18 $ 623 Three Months Ended September 30, 2020 476 (51) 39 13 477 Nine Months Ended September 30, 2021 $ 2,451 $ 188 $ 311 $ 44 $ 2,994 Nine Months Ended September 30, 2020 2,072 (19) 272 37 2,362 Southern Company Gas Southern Company Gas manages its business through four reportable segments – gas distribution operations, gas pipeline investments, wholesale gas services, and gas marketing services. The non-reportable segments are combined and presented as all other. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information on the disposition activities described herein. Gas distribution operations is the largest component of Southern Company Gas' business and includes natural gas local distribution utilities that construct, manage, and maintain intrastate natural gas pipelines and gas distribution facilities in four states. Gas pipeline investments consists of joint ventures in natural gas pipeline investments including a 50% interest in SNG, a 20% ownership interest in the PennEast Pipeline project, and a 50% joint ownership interest in the Dalton Pipeline. These natural gas pipelines enable the provision of diverse sources of natural gas supplies to the customers of Southern Company Gas. Gas pipeline investments also included a 5% ownership interest in the Atlantic Coast Pipeline construction project prior to its sale on March 24, 2020. See Note (C) under "Other Matters – Southern Company Gas" for information regarding the September 2021 cancellation of the PennEast Pipeline project. Wholesale gas services (until the sale of Sequent on July 1, 2021) provided natural gas asset management and/or related logistics services for each of Southern Company Gas' utilities except Nicor Gas as well as for non-affiliated companies. The Virginia Natural Gas asset management agreement ended on March 31, 2021 and was not extended. Additionally, wholesale gas services engaged in natural gas storage and gas pipeline arbitrage and related activities. See Note (K) under "Southern Company Gas" for information regarding the sale of Sequent on July 1, 2021. Gas marketing services provides natural gas marketing to end-use customers primarily in Georgia and Illinois through SouthStar. The all other column includes segments and subsidiaries that fall below the quantitative threshold for separate disclosure, including storage and fuels operations. The all other column included Jefferson Island through its sale on December 1, 2020 and Pivotal LNG through its sale on March 24, 2020. Business segment financial data for the three and nine months ended September 30, 2021 and 2020 was as follows: Gas Distribution Operations Gas Pipeline Investments Wholesale Gas Services (a) Gas Marketing Services Total All Other Eliminations Consolidated (in millions) Three Months Ended September 30, 2021 Operating revenues $ 556 $ 8 $ — $ 52 $ 616 $ 11 $ (4) $ 623 Segment net income (loss) (b)(c) 45 10 94 (2) 147 (91) — 56 Nine Months Ended September 30, 2021 Operating revenues $ 2,466 $ 24 $ 188 $ 311 $ 2,989 $ 29 $ (24) $ 2,994 Segment net income (loss) (b)(c)(d) 308 3 108 60 479 (90) — 389 Total assets at September 30, 2021 20,619 1,478 132 1,534 23,763 11,387 (12,192) 22,958 Three Months Ended September 30, 2020 Operating revenues $ 479 $ 8 $ (51) $ 39 $ 475 $ 8 $ (6) $ 477 Segment net income (loss) 46 23 (45) (3) 21 (7) — 14 Nine Months Ended September 30, 2020 Operating revenues $ 2,086 $ 24 $ (19) $ 272 $ 2,363 $ 24 $ (25) $ 2,362 Segment net income (loss) 284 74 (45) 59 372 (12) — 360 Total assets at December 31, 2020 19,090 1,597 850 1,503 23,040 11,336 (11,746) 22,630 (a) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) Three Months Ended September 30, 2021 $ — $ — $ — $ — $ — Three Months Ended September 30, 2020 1,050 33 1,083 1,134 (51) Nine Months Ended September 30, 2021 $ 3,881 $ 90 $ 3,971 $ 3,783 $ 188 Nine Months Ended September 30, 2020 3,089 81 3,170 3,189 (19) (b) For wholesale gas services, includes a preliminary pre-tax gain of $121 million ($93 million after tax) related to the sale of Sequent. See Note (K) under "Southern Company Gas" for additional information. (c) For the "All Other" column, includes $85 million of additional tax expense due to changes in state apportionment rates as a result of the sale of Sequent. See Note (K) under "Southern Company Gas" for additional information. (d) For gas pipeline investments, includes pre-tax impairment charges totaling $84 million ($67 million after tax) related to the equity method investment in the PennEast Pipeline project. See Notes (C) and (E) under "Other Matters – Southern Company Gas" and "Southern Company Gas," respectively, for additional information.

Introduction (Policies)

Introduction (Policies)	9 Months Ended
Introduction (Policies)	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting	The condensed quarterly financial statements of each Registrant included herein have been prepared by such Registrant, without audit, pursuant to the rules and regulations of the SEC. The Condensed Balance Sheets at December 31, 2020 have been derived from the audited financial statements of each Registrant. In the opinion of each Registrant's management, the information regarding such Registrant furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended September 30, 2021 and 2020. Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although each Registrant believes that the disclosures regarding such Registrant are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for energy and other factors, including the impacts of the COVID-19 pandemic, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year.
Reclassifications	Certain prior year data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the overall results of operations, financial position, or cash flows of any Registrant.
Goodwill	Goodwill is not amortized but is subject to an annual impairment test in the fourth quarter of the year and on an interim basis as events and changes in circumstances occur.
Natural Gas for Sale	Natural Gas for Sale With the exception of Nicor Gas, Southern Company Gas records natural gas inventories on a WACOG basis. For any declines in market prices below the WACOG considered to be other than temporary, an adjustment is recorded to reduce the value of natural gas inventories to market value. Nicor Gas' natural gas inventory is carried at cost on a LIFO basis. Inventory decrements occurring during the year that are restored prior to year end are charged to cost of natural gas at the estimated annual replacement cost. Inventory decrements that are not restored prior to year end are charged to cost of natural gas at the actual LIFO cost of the inventory layers liquidated.
Asset Retirement Obligations	The traditional electric operating companies have periodically updated, and expect to continue periodically updating, their related cost estimates and ARO liabilities for each CCR unit as additional information related to these assumptions becomes available. Some of these updates have been, and future updates may be, material. Additionally, the closure designs and plans in the States of Alabama and Georgia are subject to approval by environmental regulatory agencies. Absent continued recovery of ARO costs through regulated rates, results of operations, cash flows, and financial condition for Southern Company and the traditional electric operating companies could be materially impacted. See Note (B) under "Georgia Power – Rate Plan" for additional information. The ultimate outcome of these matters cannot be determined at this time.
Valuation Methodologies	Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and over-the-counter financial products for natural gas and physical power products, including, from time to time, basis swaps. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices, power prices, implied volatility, and overnight index swap interest rates. Interest rate derivatives are also standard over-the-counter products that are valued using observable market data and assumptions commonly used by market participants. The fair value of interest rate derivatives reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and occasionally, implied volatility of interest rate options. The fair value of cross-currency swaps reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future foreign currency exchange rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and discount rates. The interest rate derivatives and cross-currency swaps are categorized as Level 2 under Fair Value Measurements as these inputs are based on observable data and valuations of similar instruments. See Note (J) for additional information on how these derivatives are used. For fair value measurements of the investments within the nuclear decommissioning trusts and the non-qualified deferred compensation trusts, external pricing vendors are designated for each asset class with each security specifically assigned a primary pricing source. For investments held within commingled funds, fair value is determined at the end of each business day through the net asset value, which is established by obtaining the underlying securities' individual prices from the primary pricing source. A market price secured from the primary source vendor is then evaluated by management in its valuation of the assets within the trusts. As a general approach, fixed income market pricing vendors gather market data (including indices and market research reports) and integrate relative credit information, observed market movements, and sector news into proprietary pricing models, pricing systems, and mathematical tools. Dealer quotes and other market information, including live trading levels and pricing analysts' judgments, are also obtained when available. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. See Note 6 to the financial statements under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information. Southern Power has contingent payment obligations related to certain acquisitions whereby it is primarily obligated to make generation-based payments to the seller, which commenced at the commercial operation of the respective facility and continue through 2026. The obligations are categorized as Level 3 under Fair Value Measurements as
Derivatives	Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to market risks, including commodity price risk, interest rate risk, weather risk, and occasionally foreign currency exchange rate risk. To manage the volatility attributable to these exposures, each company nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to each company's policies in areas such as counterparty exposure and risk management practices. Through the sale of Sequent on July 1, 2021, Southern Company Gas' wholesale gas operations used various contracts in its commercial activities that generally met the definition of derivatives. For the traditional electric operating companies, Southern Power, and Southern Company Gas' other businesses, each company's policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note (I) for additional fair value information. In the statements of cash flows, any cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. Any cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with the classification of the hedged interest or principal, respectively. See Note 1 to the financial statements under "Financial Instruments" in Item 8 of the Form 10-K for additional information. See Note (K) under "Southern Company Gas" for information regarding Southern Company Gas' sale of Sequent. Energy-Related Derivatives The traditional electric operating companies, Southern Power, and Southern Company Gas enter into energy-related derivatives to hedge exposures to electricity, natural gas, and other fuel price changes. However, due to cost-based rate regulations and other various cost recovery mechanisms, the traditional electric operating companies and the natural gas distribution utilities have limited exposure to market volatility in energy-related commodity prices. Each of the traditional electric operating companies and certain of the natural gas distribution utilities of Southern Company Gas manage fuel-hedging programs, implemented per the guidelines of their respective state PSCs or other applicable state regulatory agencies, through the use of financial derivative contracts, which are expected to continue to mitigate price volatility. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non-exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in operating revenues. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges – Energy-related derivative contracts designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through an approved cost recovery mechanism. • Cash Flow Hedges – Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in accumulated OCI before being recognized in the statements of income in the same period and in the same income statement line item as the earnings effect of the hedged transactions. • Not Designated – Gains and losses on energy-related derivative contracts that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Some energy-related derivative contracts require physical delivery as opposed to financial settlement, and this type of derivative is both common and prevalent within the electric and natural gas industries. When an energy-related derivative contract is settled physically, any cumulative unrealized gain or loss is reversed and the contract price is recognized in the respective line item representing the actual price of the underlying goods being delivered. Interest Rate Derivatives Southern Company and certain subsidiaries may enter into interest rate derivatives to hedge exposure to changes in interest rates. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and presented on the same income statement line item as the earnings effect of the hedged transactions. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings on the same income statement line item. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Foreign Currency Derivatives Southern Company and certain subsidiaries, including Southern Power, may enter into foreign currency derivatives to hedge exposure to changes in foreign currency exchange rates, such as that arising from the issuance of debt denominated in a currency other than U.S. dollars. Derivatives related to forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and on the same income statement line as the earnings effect of the hedged transactions, including foreign currency gains or losses arising from changes in the U.S. currency exchange rates. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings on the same income statement line item, including foreign currency gains or losses arising from changes in the U.S. currency exchange rates. Southern Company has elected to exclude the cross-currency basis spread from the assessment of effectiveness in the fair value hedges of its foreign currency risk and record any difference between the change in the fair value of the excluded components and the amounts recognized in earnings as a component of OCI.

Introduction (Tables)

Introduction (Tables)	9 Months Ended
Introduction (Tables)	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Goodwill	Goodwill at September 30, 2021 and December 31, 2020 was as follows: Goodwill (in millions) Southern Company $ 5,280 Southern Company Gas: Gas distribution operations $ 4,034 Gas marketing services 981 Southern Company Gas total $ 5,015
Schedule of Other Intangible Assets, Indefinite-Lived	Other intangible assets were as follows: At September 30, 2021 At December 31, 2020 Gross Carrying Amount Accumulated Amortization Other Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 212 $ (148) $ 64 $ 212 $ (135) $ 77 Trade names 64 (36) 28 64 (31) 33 Storage and transportation contracts () — — — 64 (64) — PPA fair value adjustments 390 (104) 286 390 (89) 301 Other 10 (8) 2 10 (9) 1 Total other intangible assets subject to amortization $ 676 $ (296) $ 380 $ 740 $ (328) $ 412 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 751 $ (296) $ 455 $ 815 $ (328) $ 487 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (104) $ 286 $ 390 $ (89) $ 301 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (128) $ 28 $ 156 $ (119) $ 37 Trade names 26 (14) 12 26 (12) 14 Wholesale gas services Storage and transportation contracts () — — — 64 (64) — Total other intangible assets subject to amortization $ 182 $ (142) $ 40 $ 246 $ (195) $ 51 (*) See Note (K) under "Southern Company Gas" for information regarding the sale of Sequent.
Schedule of Other Intangible Assets, Finite-Lived	Other intangible assets were as follows: At September 30, 2021 At December 31, 2020 Gross Carrying Amount Accumulated Amortization Other Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 212 $ (148) $ 64 $ 212 $ (135) $ 77 Trade names 64 (36) 28 64 (31) 33 Storage and transportation contracts () — — — 64 (64) — PPA fair value adjustments 390 (104) 286 390 (89) 301 Other 10 (8) 2 10 (9) 1 Total other intangible assets subject to amortization $ 676 $ (296) $ 380 $ 740 $ (328) $ 412 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 751 $ (296) $ 455 $ 815 $ (328) $ 487 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (104) $ 286 $ 390 $ (89) $ 301 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (128) $ 28 $ 156 $ (119) $ 37 Trade names 26 (14) 12 26 (12) 14 Wholesale gas services Storage and transportation contracts () — — — 64 (64) — Total other intangible assets subject to amortization $ 182 $ (142) $ 40 $ 246 $ (195) $ 51 (*) See Note (K) under "Southern Company Gas" for information regarding the sale of Sequent.
Schedule of Amortization of Other Intangible Assets	Amortization associated with other intangible assets was as follows: Three Months Ended Nine Months Ended September 30, 2021 (in millions) Southern Company (a) $ 11 $ 33 Southern Power (b) 5 15 Southern Company Gas (c) 4 11 (a) Includes $5 million and $15 million for the three and nine months ended September 30, 2021, respectively, recorded as a reduction to operating revenues. (b) Recorded as a reduction to operating revenues. (c) Relates to gas marketing services.
Schedule of Restrictions on Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amount shown in the condensed statements of cash flows for the applicable Registrants: Southern Southern Power Southern September 30, 2021 December 31, 2020 September 30, 2021 September 30, 2021 December 31, 2020 (in millions) (in millions) (in millions) Cash and cash equivalents $ 2,078 $ 1,065 $ 192 $ 29 $ 17 Restricted cash (a) : Other current assets 3 2 — 3 2 Other deferred charges and assets 21 — 21 — — Total cash, cash equivalents, and restricted cash (b) $ 2,101 $ 1,068 $ 213 $ 32 $ 19 (a) For Southern Company Gas, reflects restricted cash held as collateral for workers' compensation, life insurance, and long-term disability insurance. For Southern Power, reflects restricted cash held for construction payables. (b) Total may not add due to rounding.
Schedule of Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amount shown in the condensed statements of cash flows for the applicable Registrants: Southern Southern Power Southern September 30, 2021 December 31, 2020 September 30, 2021 September 30, 2021 December 31, 2020 (in millions) (in millions) (in millions) Cash and cash equivalents $ 2,078 $ 1,065 $ 192 $ 29 $ 17 Restricted cash (a) : Other current assets 3 2 — 3 2 Other deferred charges and assets 21 — 21 — — Total cash, cash equivalents, and restricted cash (b) $ 2,101 $ 1,068 $ 213 $ 32 $ 19 (a) For Southern Company Gas, reflects restricted cash held as collateral for workers' compensation, life insurance, and long-term disability insurance. For Southern Power, reflects restricted cash held for construction payables. (b) Total may not add due to rounding.
Schedule of Changes in Asset Retirement Obligations	Details of changes in AROs for Southern Company, Alabama Power, Georgia Power, and Mississippi Power during the first nine months of 2021 are shown in the following table. There were no material changes in AROs for the other Registrants during the first nine months of 2021. Southern Company Alabama Power Georgia Mississippi Power (in millions) Balance at December 31, 2020 $ 10,684 $ 3,974 $ 6,265 $ 176 Liabilities incurred 17 — 3 — Liabilities settled (341) (152) (154) (18) Accretion 304 116 176 6 Cash flow revisions 945 385 475 30 Balance at September 30, 2021 $ 11,609 $ 4,323 $ 6,765 $ 194

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
Regulatory Matters (Tables)	Sep. 30, 2021
Regulated Operations [Abstract]
Schedule of Cost Recovery Clauses	The recovery balances for certain retail regulatory clauses of the traditional electric operating companies and Southern Company Gas at September 30, 2021 and December 31, 2020 were as follows: Regulatory Clause Balance Sheet Line Item September 30, December 31, 2020 (in millions) Alabama Power Rate CNP Compliance Other regulatory liabilities, current $ — $ 28 Other regulatory liabilities, deferred 24 — Rate CNP PPA Other regulatory assets, deferred 88 58 Retail Energy Cost Recovery Other regulatory liabilities, current — 18 Other regulatory assets, current 79 — Other regulatory assets, deferred 6 — Natural Disaster Reserve Other regulatory liabilities, deferred 36 77 Georgia Power Fuel Cost Recovery Over recovered fuel clause revenues $ — $ 113 Other deferred charges and assets 203 — Mississippi Power Fuel Cost Recovery Over recovered regulatory clause liabilities $ 5 $ 24 Ad Valorem Tax Other regulatory assets, current 12 11 Other regulatory assets, deferred 39 41 Property Damage Reserve Other regulatory liabilities, deferred — 4 Other regulatory assets, deferred 16 — Southern Company Gas Natural Gas Cost Recovery () Other regulatory liabilities $ — $ 88 Natural gas cost under recovery 432 — Other regulatory assets, deferred 79 — () The significant change during the nine months ended September 30, 2021 was primarily driven by an increase in the cost of gas purchased in February 2021 resulting from Winter Storm Uri.
Nuclear Construction Cost and Schedule	Georgia Power's approximate proportionate share of the remaining estimated capital cost to complete Plant Vogtle Units 3 and 4, including contingency, through September 2022 and June 2023, respectively, is as follows: (in millions) Base project capital cost forecast (a)(b) $ 9,342 Construction contingency estimate 137 Total project capital cost forecast (a)(b) 9,479 Net investment at September 30, 2021 (b) (8,159) Remaining estimate to complete $ 1,320 (a) Includes approximately $570 million of costs that are not shared with the other Vogtle Owners. Excludes financing costs expected to be capitalized through AFUDC of approximately $318 million, of which $169 million had been accrued through September 30, 2021. (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related customer refunds.
Schedule of Infrastructure Replacement Programs and Capital Projects	Capital expenditures incurred under specific infrastructure replacement programs during the first nine months of 2021 were as follows: Utility Program Nine Months Ended September 30, 2021 (in millions) Nicor Gas Investing in Illinois $ 307 Virginia Natural Gas Steps to Advance Virginia's Energy 36 Total $ 343

Revenue from Contracts with C_2

Revenue from Contracts with Customers and Lease Income (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	The following table disaggregates revenue from contracts with customers for the three and nine months ended September 30, 2021 and 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2021 Operating revenues Retail electric revenues Residential $ 1,974 $ 750 $ 1,138 $ 86 $ — $ — Commercial 1,432 471 882 79 — — Industrial 902 394 428 80 — — Other 24 4 18 2 — — Total retail electric revenues 4,332 1,619 2,466 247 — — Natural gas distribution revenues Residential 218 — — — — 218 Commercial 55 — — — — 55 Transportation 239 — — — — 239 Industrial 6 — — — — 6 Other 31 — — — — 31 Total natural gas distribution revenues 549 — — — — 549 Wholesale electric revenues PPA energy revenues 359 61 41 2 261 — PPA capacity revenues 125 14 14 1 97 — Non-PPA revenues 63 54 3 120 134 — Total wholesale electric revenues 547 129 58 123 492 — Other natural gas revenues Gas marketing services 45 — — — — 45 Other natural gas revenues 11 — — — — 11 Total natural gas revenues 56 — — — — 56 Other revenues 248 53 112 8 9 — Total revenue from contracts with customers 5,732 1,801 2,636 378 501 605 Other revenue sources (a) 506 103 220 — 178 18 Total operating revenues $ 6,238 $ 1,904 $ 2,856 $ 378 $ 679 $ 623 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Nine Months Ended September 30, 2021 Operating revenues Retail electric revenues Residential $ 4,910 $ 1,931 $ 2,765 $ 214 $ — $ — Commercial 3,727 1,229 2,293 205 — — Industrial 2,299 1,048 1,034 217 — — Other 70 13 51 6 — — Total retail electric revenues 11,006 4,221 6,143 642 — — Natural gas distribution revenues Residential 1,143 — — — — 1,143 Commercial 298 — — — — 298 Transportation 775 — — — — 775 Industrial 29 — — — — 29 Other 187 — — — — 187 Total natural gas distribution revenues 2,432 — — — — 2,432 Wholesale electric revenues PPA energy revenues 782 143 71 9 575 — PPA capacity revenues 375 86 41 4 247 — Non-PPA revenues 181 108 14 283 273 — Total wholesale electric revenues 1,338 337 126 296 1,095 — Other natural gas revenues Wholesale gas services 2,168 — — — — 2,168 Gas marketing services 303 — — — — 303 Other natural gas revenues 27 — — — — 27 Total natural gas revenues 2,498 — — — — 2,498 Other revenues 792 150 362 22 18 — Total revenue from contracts with customers 18,066 4,708 6,631 960 1,113 4,930 Other revenue sources (a) 2,979 311 419 28 497 1,763 Other adjustments (b) (3,699) — — — — (3,699) Total operating revenues $ 17,346 $ 5,019 $ 7,050 $ 988 $ 1,610 $ 2,994 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2020 Operating revenues Retail electric revenues Residential $ 2,019 $ 752 $ 1,183 $ 84 $ — $ — Commercial 1,354 447 833 74 — — Industrial 783 358 352 73 — — Other 22 5 15 2 — — Total retail electric revenues 4,178 1,562 2,383 233 — — Natural gas distribution revenues Residential 170 — — — — 170 Commercial 41 — — — — 41 Transportation 224 — — — — 224 Industrial 4 — — — — 4 Other 35 — — — — 35 Total natural gas distribution revenues 474 — — — — 474 Wholesale electric revenues PPA energy revenues 214 40 13 2 165 — PPA capacity revenues 136 26 15 1 95 — Non-PPA revenues 59 10 3 93 68 — Total wholesale electric revenues 409 76 31 96 328 — Other natural gas revenues Wholesale gas services 431 — — — — 431 Gas marketing services 38 — — — — 38 Other natural gas revenues 7 — — — — 7 Total natural gas revenues 476 — — — — 476 Other revenues 218 33 115 6 4 — Total revenue from contracts with customers 5,755 1,671 2,529 335 332 950 Other revenue sources (a) 968 58 88 1 191 630 Other adjustments (b) (1,103) — — — — (1,103) Total operating revenues $ 5,620 $ 1,729 $ 2,617 $ 336 $ 523 $ 477 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Nine Months Ended September 30, 2020 Operating revenues Retail electric revenues Residential $ 4,802 $ 1,839 $ 2,760 $ 203 $ — $ — Commercial 3,589 1,152 2,242 195 — — Industrial 2,081 956 907 218 — — Other 68 16 46 6 — — Total retail electric revenues 10,540 3,963 5,955 622 — — Natural gas distribution revenues Residential 906 — — — — 906 Commercial 229 — — — — 229 Transportation 723 — — — — 723 Industrial 21 — — — — 21 Other 179 — — — — 179 Total natural gas distribution revenues 2,058 — — — — 2,058 Wholesale electric revenues PPA energy revenues 550 94 38 7 425 — PPA capacity revenues 339 78 30 3 231 — Non-PPA revenues 159 33 7 235 184 — Total wholesale electric revenues 1,048 205 75 245 840 — Other natural gas revenues Wholesale gas services 1,168 — — — — 1,168 Gas marketing services 258 — — — — 258 Other natural gas revenues 22 — — — — 22 Total natural gas revenues 1,448 — — — — 1,448 Other revenues 677 117 329 19 11 — Total revenue from contracts with customers 15,771 4,285 6,359 886 851 3,506 Other revenue sources (a) 2,604 160 12 9 486 1,973 Other adjustments (b) (3,117) — — — — (3,117) Total operating revenues $ 15,258 $ 4,445 $ 6,371 $ 895 $ 1,337 $ 2,362 (a) Other revenue sources relate to revenues from customers accounted for as derivatives and leases, alternative revenue programs at Southern Company Gas, and cost recovery mechanisms and revenues that meet other scope exceptions for revenues from contracts with customers at the traditional electric operating companies. (b) Other adjustments relate to the cost of Southern Company Gas' energy and risk management activities. Wholesale gas services revenues are presented net of the related costs of those activities on the statement of income. See Notes (K) and (L) under "Southern Company Gas" for information on the sale of Sequent and components of wholesale gas services' operating revenues, respectively.
Schedule of Contract Balances	The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers at September 30, 2021 and December 31, 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivable At September 30, 2021 $ 2,343 $ 712 $ 904 $ 90 $ 170 $ 329 At December 31, 2020 2,614 632 806 77 112 788 Contract Assets At September 30, 2021 $ 165 $ 5 $ 103 $ — $ 1 $ — At December 31, 2020 158 2 71 — — — Contract Liabilities At September 30, 2021 $ 65 $ 6 $ 39 $ 1 $ 2 $ — At December 31, 2020 61 6 27 1 1 1
Schedule of Remaining Performance Obligations	Revenues from contracts with customers related to these performance obligations remaining at September 30, 2021 are expected to be recognized as follows: 2021 (remaining) 2022 2023 2024 2025 Thereafter (in millions) Southern Company $ 156 $ 543 $ 347 $ 327 $ 307 $ 2,667 Alabama Power 13 32 24 7 5 — Georgia Power 22 64 43 23 21 41 Southern Power 70 323 281 297 281 2,644
Schedule of Lease Income	Lease income for the three and nine months ended September 30, 2021 and 2020 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) For the Three Months Ended September 30, 2021 Lease income - interest income on sales-type leases $ 4 $ — $ — $ 4 $ — $ — Lease income - operating leases 56 21 11 — 21 9 Variable lease income 143 — — — 151 — Total lease income $ 203 $ 21 $ 11 $ 4 $ 172 $ 9 For the Nine Months Ended September 30, 2021 Lease income - interest income on sales-type leases $ 11 $ — $ — $ 10 $ — $ — Lease income - operating leases 168 62 31 1 64 26 Variable lease income 355 — — — 379 — Total lease income $ 534 $ 62 $ 31 $ 11 $ 443 $ 26 For the Three Months Ended September 30, 2020 Lease income - interest income on sales-type leases $ 3 $ — $ — $ 3 $ — $ — Lease income - operating leases 50 11 14 — 21 9 Variable lease income 145 — — — 153 — Total lease income $ 198 $ 11 $ 14 $ 3 $ 174 $ 9 For the Nine Months Ended September 30, 2020 Lease income - interest income on sales-type leases $ 8 $ — $ — $ 8 $ — $ — Lease income - operating leases 148 24 44 1 66 26 Variable lease income 345 — — — 368 — Total lease income $ 501 $ 24 $ 44 $ 9 $ 434 $ 26
Undiscounted Cash Flows to be Received Under Sales-type Leases	The undiscounted cash flows expected to be received by Southern Power for assets under the lease are as follows: At September 30, 2021 (in millions) 2021 (remaining) $ 2 2022 8 2023 8 2024 8 2025 8 2026 8 Thereafter 115 Total undiscounted cash flows $ 157 Net investment in sales-type lease () 99 Difference between undiscounted cash flows and discounted cash flows $ 58 () Included in other current assets and other property and investments on the balance sheet.

Consolidated Entities and Equ_2

Consolidated Entities and Equity Method Investments (Tables)	9 Months Ended
	Sep. 30, 2021
Regulated Operations [Abstract]
Schedule of Equity Method Investments	The carrying amounts of Southern Company Gas' equity method investments at September 30, 2021 and December 31, 2020 and related earnings (loss) from those investments for the three and nine months ended September 30, 2021 and 2020 were as follows: Investment Balance September 30, 2021 December 31, 2020 (in millions) SNG $ 1,130 $ 1,167 PennEast Pipeline () 11 91 Other 33 32 Total $ 1,174 $ 1,290 () Investment balance at September 30, 2021 reflects pre-tax impairment charges totaling $84 million recorded during 2021. See Note (C) under "Other Matters – Southern Company Gas" for additional information, including the September 2021 cancellation of the project.
Schedule of Earnings (Loss) from Equity Method Investments	Three Months Ended September 30, Nine Months Ended September 30, Earnings (Loss) from Equity Method Investments 2021 2020 2021 2020 (in millions) SNG $ 27 $ 30 $ 93 $ 95 PennEast Pipeline (a)(b) (2) 2 (81) 5 Other (a)(c) — 1 2 6 Total $ 25 $ 33 $ 14 $ 106 (a) Earnings primarily result from AFUDC equity recorded by the project entity. (b) Includes pre-tax impairment charges totaling $2 million and $84 million for the three and nine months ended September 30, 2021, respectively. See Note (C) under "Other Matters – Southern Company Gas" for additional information, including the September 2021 cancellation of the project. (c) On March 24, 2020, Southern Company Gas completed the sale of its interests in Atlantic Coast Pipeline and Pivotal LNG. See Note 15 to the financial statements under "Southern Company Gas" in Item 8 of the Form 10-K for additional information.

Financing (Tables)

Financing (Tables)	9 Months Ended
Financing (Tables)	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Credit Arrangements	At September 30, 2021, committed credit arrangements with banks were as follows: Expires Company 2022 2023 2024 2026 Total Unused Due within One Year (in millions) Southern Company parent $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — Alabama Power — — 550 700 1,250 1,250 — Georgia Power — — — 1,750 1,750 1,726 — Mississippi Power — 125 150 — 275 250 — Southern Power (a) — — — 600 600 568 — Southern Company Gas (b) 250 — — 1,500 1,750 1,747 250 SEGCO 30 — — — 30 30 30 Southern Company $ 280 $ 125 $ 700 $ 6,550 $ 7,655 $ 7,570 $ 280 (a) Does not include Southern Power Company's $75 million and $60 million continuing letter of credit facilities for standby letters of credit expiring in 2023, of which $23 million and $1 million, respectively, was unused at September 30, 2021. Southern Power's subsidiaries are not parties to its bank credit arrangements or letter of credit facilities. (b) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $800 million of the arrangement expiring in 2026 and all $250 million of the arrangement expiring in 2022. Southern Company Gas' committed credit arrangement expiring in 2026 also includes $700 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas. Pursuant to the multi-year credit arrangement expiring in 2026, the allocations between Southern Company Gas Capital and Nicor Gas may be adjusted.
Schedule of Shares Used to Compute Diluted Earnings Per Share	Shares used to compute diluted earnings per share were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in millions) As reported shares 1,061 1,058 1,060 1,058 Effect of stock-based compensation 7 6 7 6 Diluted shares 1,068 1,064 1,067 1,064

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
Income Taxes (Tables)	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Summary of Operating Loss Carryforwards Valuation Allowances	Details of significant changes in valuation allowances for the applicable Registrants are provided below: Southern Company Georgia Power (in millions) Federal $ 20 $ — State (net of federal benefit) 92 28 Balance at December 31, 2020 $ 112 $ 28 Federal $ 20 $ — State (net of federal benefit) 122 58 Balance at September 30, 2021 $ 142 $ 58

Retirement Benefits (Tables)

Retirement Benefits (Tables)	9 Months Ended
Retirement Benefits (Tables)	Sep. 30, 2021
Retirement Benefits [Abstract]
Schedule of Pension Plans and Postretirement Plans	Components of the net periodic benefit costs for the three and nine months ended September 30, 2021 and 2020 are presented in the following tables. Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2021 Pension Plans Service cost $ 109 $ 26 $ 28 $ 4 $ 2 $ 10 Interest cost 87 20 26 4 2 6 Expected return on plan assets (298) (72) (94) (14) (4) (21) Amortization: Prior service costs — — — — — (1) Regulatory asset — — — — — 3 Net (gain)/loss 78 21 25 4 1 3 Net periodic pension cost (income) $ (24) $ (5) $ (15) $ (2) $ 1 $ — Postretirement Benefits Service cost $ 6 $ 2 $ 2 $ 1 $ 1 $ — Interest cost 9 2 3 — — 1 Expected return on plan assets (19) (8) (7) (1) — (2) Amortization: Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ (3) $ (4) $ (1) $ — $ 1 $ — Nine Months Ended September 30, 2021 Pension Plans Service cost $ 326 $ 77 $ 84 $ 13 $ 7 $ 28 Interest cost 260 61 78 12 4 18 Expected return on plan assets (893) (215) (282) (41) (11) (64) Amortization: Prior service costs — — 1 — — (2) Regulatory asset — — — — — 11 Net (gain)/loss 235 62 75 11 3 9 Net periodic pension cost (income) $ (72) $ (15) $ (44) $ (5) $ 3 $ — Postretirement Benefits Service cost $ 18 $ 5 $ 5 $ 1 $ 1 $ 1 Interest cost 26 6 9 1 — 3 Expected return on plan assets (57) (22) (20) (2) — (6) Amortization: Prior service costs (1) — — — — — Regulatory asset — — — — — 5 Net (gain)/loss 3 — 2 — — (2) Net periodic postretirement benefit cost (income) $ (11) $ (11) $ (4) $ — $ 1 $ 1 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Three Months Ended September 30, 2020 Pension Plans Service cost $ 94 $ 23 $ 24 $ 3 $ 2 $ 8 Interest cost 108 25 33 5 1 8 Expected return on plan assets (274) (66) (87) (13) (4) (20) Amortization: Prior service costs — 1 — — — (1) Regulatory asset — — — — — 4 Net (gain)/loss 67 17 22 4 1 2 Net periodic pension cost (income) $ (5) $ — $ (8) $ (1) $ — $ 1 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ (1) $ 1 $ — Interest cost 13 4 5 1 — 2 Expected return on plan assets (18) (7) (7) — — (2) Amortization: Prior service costs — — (1) — — — Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ 2 $ (2) $ — $ — $ 1 $ 1 Nine Months Ended September 30, 2020 Pension Plans Service cost $ 282 $ 67 $ 72 $ 11 $ 6 $ 24 Interest cost 324 75 100 15 4 23 Expected return on plan assets (824) (198) (261) (38) (10) (59) Amortization: Prior service costs 1 1 1 — — (2) Regulatory asset — — — — — 12 Net (gain)/loss 201 53 65 10 2 7 Net periodic pension cost (income) $ (16) $ (2) $ (23) $ (2) $ 2 $ 5 Postretirement Benefits Service cost $ 17 $ 4 $ 5 $ — $ 1 $ 1 Interest cost 40 10 15 2 — 5 Expected return on plan assets (54) (21) (20) (1) — (5) Amortization: Prior service costs (1) — (1) — — — Regulatory asset — — — — — 5 Net (gain)/loss 2 — 2 — — (2) Net periodic postretirement benefit cost (income) $ 4 $ (7) $ 1 $ 1 $ 1 $ 4

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
Fair Value Measurements (Tables)	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value	At September 30, 2021, assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using: At September 30, 2021 Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 75 $ 425 $ — $ — $ 500 Interest rate derivatives — 25 — — 25 Foreign currency derivatives — 20 — — 20 Investments in trusts: (b)(c) Domestic equity 738 237 — — 975 Foreign equity 167 183 — — 350 U.S. Treasury and government agency securities — 352 — — 352 Municipal bonds — 48 — — 48 Pooled funds – fixed income — 14 — — 14 Corporate bonds 2 472 — — 474 Mortgage and asset backed securities — 92 — — 92 Private equity — — — 123 123 Cash and cash equivalents 5 — — — 5 Other 29 13 — — 42 Cash equivalents 1,498 9 — — 1,507 Other investments 9 26 — — 35 Total $ 2,523 $ 1,916 $ — $ 123 $ 4,562 Liabilities: Energy-related derivatives (a) $ 27 $ 17 $ — $ — $ 44 Interest rate derivatives — 16 — — 16 Foreign currency derivatives — 43 — — 43 Contingent consideration — — 16 — 16 Other — 13 — — 13 Total $ 27 $ 89 $ 16 $ — $ 132 Fair Value Measurements Using: At September 30, 2021 Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 104 $ — $ — $ 104 Interest rate derivatives — 5 — — 5 Nuclear decommissioning trusts: (b) Domestic equity 444 227 — — 671 Foreign equity 167 — — — 167 U.S. Treasury and government agency securities — 22 — — 22 Municipal bonds — 1 — — 1 Corporate bonds 2 243 — — 245 Mortgage and asset backed securities — 22 — — 22 Private equity — — — 123 123 Other 6 — — — 6 Cash equivalents 443 9 — — 452 Other investments — 26 — — 26 Total $ 1,062 $ 659 $ — $ 123 $ 1,844 Liabilities: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Georgia Power Assets: Energy-related derivatives $ — $ 166 $ — $ — $ 166 Nuclear decommissioning trusts: (b)(c) Domestic equity 294 1 — — 295 Foreign equity — 180 — — 180 U.S. Treasury and government agency securities — 330 — — 330 Municipal bonds — 47 — — 47 Corporate bonds — 229 — — 229 Mortgage and asset backed securities — 70 — — 70 Other 23 13 — — 36 Cash equivalents 240 — — — 240 Total $ 557 $ 1,036 $ — $ — $ 1,593 Liabilities: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Fair Value Measurements Using: At September 30, 2021 Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 105 $ — $ — $ 105 Cash equivalents 121 — — — 121 Total $ 121 $ 105 $ — $ — $ 226 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Southern Power Assets: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Foreign currency derivatives — 20 — — 20 Total $ — $ 30 $ — $ — $ 30 Liabilities: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Foreign currency derivatives — 11 — — 11 Contingent consideration — — 16 — 16 Other — 13 — — 13 Total $ — $ 26 $ 16 $ — $ 42 Southern Company Gas Assets: Energy-related derivatives (a) $ 75 $ 40 $ — $ — $ 115 Interest rate derivatives — 6 — — 6 Non-qualified deferred compensation trusts: Domestic equity — 9 — — 9 Foreign equity — 3 — — 3 Pooled funds – fixed income — 14 — — 14 Cash equivalents 5 — — — 5 Total $ 80 $ 72 $ — $ — $ 152 Liabilities: Energy-related derivatives (a) $ 27 $ 4 $ — $ — $ 31 Interest rate derivatives — 4 — — 4 Total $ 27 $ 8 $ — $ — $ 35 (a) Excludes cash collateral of $(20) million. (b) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. (c) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. At September 30, 2021, approximately $57 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information.
Schedule of Increase (Decrease) In Fair Value Of Funds	The fair value of the funds, including reinvested interest and dividends and excluding the funds' expenses, increased (decreased) by the amounts shown in the table below for the nine months ended September 30, 2021 and 2020. The changes were recorded as a change to the regulatory assets and liabilities related to AROs for Georgia Power and Alabama Power, respectively. Fair value increases (decreases) Three Months Ended September 30, 2021 Three Months Ended September 30, 2020 Nine Months Ended September 30, 2021 Nine Months Ended September 30, 2020 (in millions) Southern Company $ 9 $ 108 $ 173 $ 85 Alabama Power 15 66 133 24 Georgia Power (6) 42 40 61
Schedule of Financial Instruments for which Carrying Amount Did Not Equal Fair Value	At September 30, 2021, other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas () (in billions) Long-term debt, including securities due within one year: Carrying amount $ 51.9 $ 9.1 $ 13.6 $ 1.6 $ 4.0 $ 6.8 Fair value 57.6 10.4 15.2 1.7 4.4 7.8 () The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the 2016 merger with Southern Company. Southern Company Gas amortizes the fair value adjustments over the remaining lives of the respective bonds, the latest being through 2043.
Schedule of Fair Value of Commodity Derivative Contracts that Include a Significant Unobservable Component	The following table provides a reconciliation of Southern Company Gas' Level 3 contracts during the three and nine months ended September 30, 2021. Three Months Ended September 30, 2021 Nine Months Ended September 30, 2021 (in millions) Beginning balance $ 18 $ 28 Instruments realized or otherwise settled during period — (6) Changes in fair value — (4) Sale of Sequent (18) (18) Ending balance $ — $ —

Derivatives (Tables)

Derivatives (Tables)	9 Months Ended
Derivatives (Tables)	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Energy-Related Derivatives	At September 30, 2021, the net volume of energy-related derivative contracts for natural gas positions, together with the longest hedge date over which the respective entity is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Net Longest Longest (in millions) Southern Company () 336 2030 2024 Alabama Power 75 2024 — Georgia Power 99 2024 — Mississippi Power 79 2025 — Southern Power 6 2030 2022 Southern Company Gas () 77 2024 2024 (*) Southern Company Gas' derivative instruments include both long and short natural gas positions. A long position is a contract to purchase natural gas and a short position is a contract to sell natural gas. Southern Company Gas' volume represents the net of long natural gas positions of 91.4 million mmBtu and short natural gas positions of 14.3 million mmBtu at September 30, 2021, which is also included in Southern Company's total volume. See Note (K) under "Southern Company Gas" for information regarding Southern Company Gas' sale of Sequent.
Schedule of Interest Rate Derivatives	At September 30, 2021, the following interest rate derivatives were outstanding: Notional Interest Weighted Hedge Fair Value Gain (Loss) at September 30, 2021 (in millions) (in millions) Cash Flow Hedges of Forecasted Debt Alabama Power $ 150 — 1.91% August 2051 $ 5 Fair Value Hedges of Existing Debt Southern Company parent 400 1.75% 1-month LIBOR + 0.68% March 2028 (2) Southern Company parent 1,000 3.70% 1-month LIBOR + 2.36% April 3 Southern Company Gas 500 1.75% 1-month LIBOR + 0.38% January 2031 2 Southern Company $ 2,050 $ 8
Schedule of Foreign Currency Derivatives	At September 30, 2021, the following foreign currency derivatives were outstanding: Pay Notional Pay Receive Notional Receive Hedge Fair Value Gain (Loss) at September 30, 2021 (in millions) (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company parent $ 1,476 3.39% € 1,250 1.88% September 2027 $ (32) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 9 Southern Power 564 3.78% 500 1.85% June 2026 — Southern Power total $ 1,241 € 1,100 $ 9 Southern Company $ 2,717 € 2,350 $ (23)
Schedule of Derivative Category and Balance Sheet Location	The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 308 $ 9 $ 24 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 118 6 18 19 Total derivatives designated as hedging instruments for regulatory purposes $ 426 $ 15 $ 42 $ 30 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 41 $ — $ 3 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 4 — — — Interest rate derivatives: Assets from risk management activities/Other current liabilities 25 — 20 — Other deferred charges and assets/Other deferred credits and liabilities — 16 — — Foreign currency derivatives: Assets from risk management activities/Other current liabilities 9 33 — 23 Other deferred charges and assets/Other deferred credits and liabilities 11 10 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 90 $ 59 $ 110 $ 28 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 29 $ 29 $ 388 $ 331 Other deferred charges and assets/Other deferred credits and liabilities 1 — 270 232 Total derivatives not designated as hedging instruments $ 30 $ 29 $ 658 $ 563 Gross amounts recognized $ 546 $ 103 $ 810 $ 621 Gross amounts offset (a) (57) (37) (529) (557) Net amounts recognized in the Balance Sheets (b) $ 489 $ 66 $ 281 $ 64 At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 67 $ 2 $ 7 $ 2 Other deferred charges and assets/Other deferred credits and liabilities 37 2 5 5 Total derivatives designated as hedging instruments for regulatory purposes $ 104 $ 4 $ 12 $ 7 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ 5 $ — $ — $ — Gross amounts recognized $ 109 $ 4 $ 12 $ 7 Gross amounts offset (3) (3) (7) (7) Net amounts recognized in the Balance Sheets $ 106 $ 1 $ 5 $ — Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 124 $ 2 $ 7 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 42 2 8 8 Total derivatives designated as hedging instruments for regulatory purposes $ 166 $ 4 $ 15 $ 13 Gross amounts recognized $ 166 $ 4 $ 15 $ 13 Gross amounts offset (3) (3) (12) (12) Net amounts recognized in the Balance Sheets $ 163 $ 1 $ 3 $ 1 Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 66 $ 1 $ 4 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 39 2 5 6 Total derivatives designated as hedging instruments for regulatory purposes $ 105 $ 3 $ 9 $ 9 Gross amounts recognized $ 105 $ 3 $ 9 $ 9 Gross amounts offset (2) (2) (7) (7) Net amounts recognized in the Balance Sheets $ 103 $ 1 $ 2 $ 2 At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 8 $ — $ 2 $ 2 Other deferred charges and assets/Other deferred credits and liabilities 1 — — — Foreign currency derivatives: Other current assets/Other current liabilities 9 11 — 23 Other deferred charges and assets/Other deferred credits and liabilities 11 — 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 29 $ 11 $ 89 $ 25 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 2 $ — $ 1 Total derivatives not designated as hedging instruments $ 1 $ 2 $ — $ 1 Gross amounts recognized $ 30 $ 13 $ 89 $ 26 Gross amounts offset (1) (1) — — Net amounts recognized in the Balance Sheets $ 29 $ 12 $ 89 $ 26 At September 30, 2021 At December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 51 $ 4 $ 6 $ 1 Total derivatives designated as hedging instruments for regulatory purposes $ 51 $ 4 $ 6 $ 1 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 33 $ — $ 1 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 3 — — — Interest rate derivatives: Assets from risk management activities/Liabilities from risk management activities-current 6 — — — Other deferred charges and assets/Other deferred credits and liabilities — 4 — — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 42 $ 4 $ 1 $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 28 $ 27 $ 388 $ 330 Other deferred charges and assets/Other deferred credits and liabilities 1 — 270 232 Total derivatives not designated as hedging instruments $ 29 $ 27 $ 658 $ 562 Gross amounts recognized $ 122 $ 35 $ 665 $ 566 Gross amounts offset (a) (48) (28) (503) (531) Net amounts recognized in the Balance Sheets (b) $ 74 $ 7 $ 162 $ 35 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $(20) million and $28 million at September 30, 2021 and December 31, 2020, respectively. (b) Net amounts of derivative instruments outstanding exclude immaterial premium and intrinsic value associated with weather derivatives for both periods presented.
Schedule of Pre-tax Effects of Unrealized Derivative Gains (Losses)	At September 30, 2021 and December 31, 2020, the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) At September 30, 2021: Energy-related derivatives: Other regulatory assets, current $ (5) $ (1) $ (1) $ — $ (3) Other regulatory liabilities, current 297 66 123 66 42 Other regulatory liabilities, deferred 112 35 40 37 — Total energy-related derivative gains (losses) $ 404 $ 100 $ 162 $ 103 $ 39 At December 31, 2020: Energy-related derivatives: Other regulatory assets, deferred $ (2) $ — $ (1) $ (1) $ — Other regulatory liabilities, current 12 5 2 1 4 Other regulatory liabilities, deferred 2 1 1 — — Total energy-related derivative gains (losses) $ 12 $ 6 $ 2 $ — $ 4
Schedule of Pre-Tax Effects of Hedging on AOCI	For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of cash flow and fair value hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months Ended September 30, For the Nine Months Ended September 30, 2021 2020 2021 2020 (in millions) (in millions) Southern Company Cash flow hedges: Energy-related derivatives $ 38 $ 9 $ 59 $ 2 Interest rate derivatives 5 1 7 (27) Foreign currency derivatives (36) 54 (79) (10) Fair value hedges () : Foreign currency derivatives (4) — (4) — Total $ 3 $ 64 $ (17) $ (35) Southern Power Cash flow hedges: Energy-related derivatives $ 8 $ 5 $ 16 $ 2 Foreign currency derivatives (36) 54 (79) (10) Total $ (28) $ 59 $ (63) $ (8) Southern Company Gas Cash flow hedges: Energy-related derivatives $ 30 $ 4 $ 43 $ — Interest rate derivatives — 1 — (24) Total $ 30 $ 5 $ 43 $ (24) () Represents amounts excluded from the assessment of effectiveness for which the difference between changes in fair value and periodic amortization is recorded in OCI.
Schedule of Pre-Tax Effects of Cash Flow and Fair Value Hedging on Income	For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of cash flow and fair value hedge accounting on income were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months Ended September 30, For the Nine Months Ended September 30, 2021 2020 2021 2020 (in millions) (in millions) Southern Company Total cost of natural gas $ 129 $ 71 $ 943 $ 654 Gain (loss) on energy-related cash flow hedges (a) 2 — — (8) Total depreciation and amortization 896 889 2,658 2,619 Gain (loss) on energy-related cash flow hedges (a) 3 (1) 6 (3) Total interest expense, net of amounts capitalized (451) (443) (1,352) (1,343) Gain (loss) on interest rate cash flow hedges (a) (7) (6) (20) (19) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) (18) (18) Gain (loss) on interest rate fair value hedges (b) (4) (3) (16) 27 Total other income (expense), net 131 113 297 319 Gain (loss) on foreign currency cash flow hedges (a)(c) (34) 56 (76) 52 Gain (loss) on foreign currency fair value hedges (32) — (32) — Amount excluded from effectiveness testing recognized in earnings 4 — 4 — Southern Power Total depreciation and amortization $ 132 $ 129 $ 383 $ 367 Gain (loss) on energy-related cash flow hedges (a) 3 (1) 6 (3) Total interest expense, net of amounts capitalized (36) (36) (111) (114) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) (18) (18) Total other income (expense), net 2 13 10 19 Gain (loss) on foreign currency cash flow hedges (a)(c) (34) 56 (76) 52 (a) Reclassified from accumulated OCI into earnings. (b) For fair value hedges, changes in the fair value of the derivative contracts are generally equal to changes in the fair value of the underlying debt and have no material impact on income. (c) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes.
Schedule of Cumulative Basis Adjustments for Fair Value Hedges	At September 30, 2021 and December 31, 2020, the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items At September 30, 2021 At December 31, 2020 At September 30, 2021 At December 31, 2020 (in millions) (in millions) Southern Company Securities due within one year $ — $ (1,509) $ — $ (10) Long-term debt (3,320) — — — Southern Company Gas Long-term debt $ (497) $ — $ (1) $ —
Schedule of Pre-tax Effect of Interest Rate and Energy Related Derivatives on Income	For the three and nine months ended September 30, 2021 and 2020, the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income of Southern Company and Southern Company Gas were as follows: Gain (Loss) Three Months Ended September 30, Nine Months Ended September 30, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2021 2020 2021 2020 (in millions) (in millions) Energy-related derivatives: Natural gas revenues () $ (2) $ (30) $ (122) $ 54 Cost of natural gas 20 5 36 18 Total derivatives in non-designated hedging relationships $ 18 $ (25) $ (86) $ 72 () Excludes immaterial gains (losses) recorded in natural gas revenues associated with weather derivatives for all periods presented.

Acquisitions and Dispositions (

Acquisitions and Dispositions (Tables)	9 Months Ended
Acquisitions and Dispositions (Tables)	Sep. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Schedule of Asset Acquisitions	During the nine months ended September 30, 2021, Southern Power acquired a controlling membership interest in the wind facility listed below. Acquisition-related costs were expensed as incurred and were not material. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Contract Period Deuel Harvest () Wind Invenergy Renewables, LLC 300 Deuel County, SD 100% of Class B February 2021 25 years and 15 years () On March 26, 2021, Southern Power acquired a controlling interest in the project from Invenergy Renewables LLC and, on March 30, 2021, Southern Power completed a tax equity transaction whereby it sold the Class A membership interests in the project. Southern Power consolidates the project's operating results in its financial statements and the tax equity partner and Invenergy Renewables LLC each own a noncontrolling interest.
Schedule of Construction Projects	Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Projects Under Construction at September 30, 2021 Garland Solar Storage (a) Battery energy storage system 88 Kern County, CA September 2021 and fourth quarter 2021 (b) 20 years Tranquillity Solar Storage (a) Battery energy storage system 72 Fresno County, CA Fourth quarter 2021 and 20 years Glass Sands (c) Wind 118 Murray County, OK Fourth quarter 2021 12 years (a) During the third quarter 2021, Southern Power further restructured its ownership in the Garland and Tranquillity battery energy storage projects and completed tax equity transactions whereby it sold the Class A membership interests in the projects. Southern Power consolidates each project's operating results in its financial statements and the tax equity partner and two other partners each own a noncontrolling interest. (b) The facility has a total capacity of 88 MWs, of which 45 MWs were placed in service in September 2021 and 43 MWs are expected to be placed in service later in the fourth quarter 2021. (c) In December 2020, Southern Power purchased 100% of the membership interests of the Glass Sands facility.
Schedule of Assets Held for Sale	The following table provides the major classes of assets classified as held for sale by Southern Company at September 30, 2021 and December 31, 2020: Southern Company At September 30, At December 31, 2021 2020 (in millions) Assets Held for Sale: Total property, plant, and equipment $ 6 $ 8 Leveraged leases 45 52 Total Assets Held for Sale $ 51 $ 60

Segment and Related Informati_2

Segment and Related Information (Tables)	9 Months Ended
Segment and Related Information (Tables)	Sep. 30, 2021
Segment Reporting [Abstract]
Schedule of Financial Data for Business Segments	Financial data for business segments and products and services for the three and nine months ended September 30, 2021 and 2020 was as follows: Electric Utilities Traditional Southern Eliminations Total Southern Company Gas All Eliminations Consolidated (in millions) Three Months Ended September 30, 2021 Operating revenues $ 5,018 $ 679 $ (170) $ 5,527 $ 623 $ 124 $ (36) $ 6,238 Segment net income (loss) (a)(b)(c) 1,085 78 — 1,163 56 (121) 3 1,101 Nine Months Ended September 30, 2021 Operating revenues $ 12,813 $ 1,610 $ (372) $ 14,051 $ 2,994 $ 412 $ (111) $ 17,346 Segment net income (loss) (a)(b)(c)(d)(e)(f) 2,352 211 — 2,563 389 (338) (6) 2,608 At September 30, 2021 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Assets held for sale 3 — — 3 — 48 — 51 Total assets 89,057 13,611 (708) 101,960 22,958 3,704 (761) 127,861 Three Months Ended September 30, 2020 Operating revenues $ 4,629 $ 523 $ (103) $ 5,049 $ 477 $ 132 $ (38) $ 5,620 Segment net income (loss) (a) 1,284 74 — 1,358 14 (122) 1 1,251 Nine Months Ended September 30, 2020 Operating revenues $ 11,576 $ 1,337 $ (285) $ 12,628 $ 2,362 $ 380 $ (112) $ 15,258 Segment net income (loss) (a)(c)(f)(g) 2,571 212 — 2,783 360 (420) 9 2,732 At December 31, 2020 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Assets held for sale 5 — — 5 — 55 — 60 Total assets 85,486 13,235 (680) 98,041 22,630 3,168 (904) 122,935 (a) Attributable to Southern Company. (b) For Southern Company Gas, includes a preliminary pre-tax gain of $121 million ($93 million after tax) related to its sale of Sequent, as well as the resulting $85 million of additional tax expense due to changes in state apportionment rates. See Note (K) under "Southern Company Gas" for additional information. (c) For the traditional electric operating companies, includes pre-tax charges at Georgia Power for estimated losses associated with the construction of Plant Vogtle Units 3 and 4 of $264 million ($197 million after tax) and $772 million ($576 million after tax) for the three and nine months ended September 30, 2021, respectively, and $149 million ($111 million after tax) for the nine months ended September 30, 2020. See Note (B) and Note 2 to the financial statements in Item 8 of the Form 10-K under "Georgia Power – Nuclear Construction" for additional information. (d) For Southern Power, includes gains on wind turbine equipment contributed to various equity method investments totaling approximately $37 million pre-tax ($28 million after tax). See Notes (E) and (K) under "Southern Power" for additional information. (e) For Southern Company Gas, includes pre-tax impairment charges totaling $84 million ($67 million after tax) related to its equity method investment in the PennEast Pipeline project. See Notes (C) and (E) under "Other Matters – Southern Company Gas" and "Southern Company Gas," respectively, for additional information. (f) For the "All Other" column, includes pre-tax impairment charges related to leveraged lease investments of $7 million ($6 million after tax) and $154 million ($74 million after tax) for the nine months ended September 30, 2021 and 2020, respectively. See Note 3 to the financial statements in Item 8 of the Form 10-K under "Other Matters – Southern Company" for additional information. (g) For Southern Power, includes a $39 million pre-tax gain ($23 million gain after tax) on the sale of Plant Mankato. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Power" for additional information. Business segment financial data for the three and nine months ended September 30, 2021 and 2020 was as follows: Gas Distribution Operations Gas Pipeline Investments Wholesale Gas Services (a) Gas Marketing Services Total All Other Eliminations Consolidated (in millions) Three Months Ended September 30, 2021 Operating revenues $ 556 $ 8 $ — $ 52 $ 616 $ 11 $ (4) $ 623 Segment net income (loss) (b)(c) 45 10 94 (2) 147 (91) — 56 Nine Months Ended September 30, 2021 Operating revenues $ 2,466 $ 24 $ 188 $ 311 $ 2,989 $ 29 $ (24) $ 2,994 Segment net income (loss) (b)(c)(d) 308 3 108 60 479 (90) — 389 Total assets at September 30, 2021 20,619 1,478 132 1,534 23,763 11,387 (12,192) 22,958 Three Months Ended September 30, 2020 Operating revenues $ 479 $ 8 $ (51) $ 39 $ 475 $ 8 $ (6) $ 477 Segment net income (loss) 46 23 (45) (3) 21 (7) — 14 Nine Months Ended September 30, 2020 Operating revenues $ 2,086 $ 24 $ (19) $ 272 $ 2,363 $ 24 $ (25) $ 2,362 Segment net income (loss) 284 74 (45) 59 372 (12) — 360 Total assets at December 31, 2020 19,090 1,597 850 1,503 23,040 11,336 (11,746) 22,630 (a) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) Three Months Ended September 30, 2021 $ — $ — $ — $ — $ — Three Months Ended September 30, 2020 1,050 33 1,083 1,134 (51) Nine Months Ended September 30, 2021 $ 3,881 $ 90 $ 3,971 $ 3,783 $ 188 Nine Months Ended September 30, 2020 3,089 81 3,170 3,189 (19) (b) For wholesale gas services, includes a preliminary pre-tax gain of $121 million ($93 million after tax) related to the sale of Sequent. See Note (K) under "Southern Company Gas" for additional information. (c) For the "All Other" column, includes $85 million of additional tax expense due to changes in state apportionment rates as a result of the sale of Sequent. See Note (K) under "Southern Company Gas" for additional information. (d) For gas pipeline investments, includes pre-tax impairment charges totaling $84 million ($67 million after tax) related to the equity method investment in the PennEast Pipeline project. See Notes (C) and (E) under "Other Matters – Southern Company Gas" and "Southern Company Gas," respectively, for additional information.
Schedule of Financial Data for Products and Services	Electric Utilities' Revenues Retail Wholesale Other Total (in millions) Three Months Ended September 30, 2021 $ 4,551 $ 731 $ 245 $ 5,527 Three Months Ended September 30, 2020 4,243 584 222 5,049 Nine Months Ended September 30, 2021 $ 11,492 $ 1,822 $ 737 $ 14,051 Nine Months Ended September 30, 2020 10,503 1,473 652 12,628 Southern Company Gas' Revenues Gas Wholesale Gas Services () Gas Other Total (in millions) Three Months Ended September 30, 2021 $ 553 $ — $ 52 $ 18 $ 623 Three Months Ended September 30, 2020 476 (51) 39 13 477 Nine Months Ended September 30, 2021 $ 2,451 $ 188 $ 311 $ 44 $ 2,994 Nine Months Ended September 30, 2020 2,072 (19) 272 37 2,362 () The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. See "Southern Company Gas" herein for additional information. Also see Note (K) under "Southern Company Gas" regarding the July 1, 2021 sale of Sequent.

Introduction - Schedule of Good

Introduction - Schedule of Goodwill (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Goodwill [Line Items]
Goodwill	$ 5,280	$ 5,280
SOUTHERN Co GAS
Goodwill [Line Items]
Goodwill	5,015	5,015
SOUTHERN Co GAS \| Gas distribution operations
Goodwill [Line Items]
Goodwill	4,034	4,034
SOUTHERN Co GAS \| Gas marketing services
Goodwill [Line Items]
Goodwill	$ 981	$ 981

Introduction - Schedule of Othe

Introduction - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Other intangible assets subject to amortization:
Gross Carrying Amount	$ 676	$ 740
Accumulated Amortization	(296)	(328)
Other Intangible Assets, Net	380	412
Other intangible assets not subject to amortization:
Federal Communications Commission licenses	75	75
Total other intangible assets
Gross Carrying Amount	751	815
Accumulated Amortization	(296)	(328)
Other Intangible Assets, Net	455	487
Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	212	212
Accumulated Amortization	(148)	(135)
Other Intangible Assets, Net	64	77
Total other intangible assets
Accumulated Amortization	(148)	(135)
Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(36)	(31)
Other Intangible Assets, Net	28	33
Total other intangible assets
Accumulated Amortization	(36)	(31)
Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	0	64
Accumulated Amortization	0	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	0	(64)
PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(104)	(89)
Other Intangible Assets, Net	286	301
Total other intangible assets
Accumulated Amortization	(104)	(89)
Other
Other intangible assets subject to amortization:
Gross Carrying Amount	10	10
Accumulated Amortization	(8)	(9)
Other Intangible Assets, Net	2	1
Total other intangible assets
Accumulated Amortization	(8)	(9)
SOUTHERN POWER CO
Other intangible assets subject to amortization:
Accumulated Amortization	(104)	(89)
Total other intangible assets
Accumulated Amortization	(104)	(89)
SOUTHERN POWER CO \| PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(104)	(89)
Other Intangible Assets, Net	286	301
Total other intangible assets
Accumulated Amortization	(104)	(89)
SOUTHERN Co GAS
Other intangible assets subject to amortization:
Gross Carrying Amount	182	246
Accumulated Amortization	(142)	(195)
Other Intangible Assets, Net	40	51
Total other intangible assets
Accumulated Amortization	(142)	(195)
Other Intangible Assets, Net	40	51
SOUTHERN Co GAS \| Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(128)	(119)
Other Intangible Assets, Net	28	37
Total other intangible assets
Accumulated Amortization	(128)	(119)
SOUTHERN Co GAS \| Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(14)	(12)
Other Intangible Assets, Net	12	14
Total other intangible assets
Accumulated Amortization	(14)	(12)
SOUTHERN Co GAS \| Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	0	64
Accumulated Amortization	0	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	$ 0	$ (64)

Introduction - Schedule of Amor

Introduction - Schedule of Amortization of Other Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 11	$ 33
Decrease in operating revenues	5	15
SOUTHERN POWER CO
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	5	15
SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 4	$ 11

Introduction - Schedule of Cash

Introduction - Schedule of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 2,078	$ 1,065
Restricted cash:
Total cash, cash equivalents, and restricted cash	2,101	1,068	$ 3,383	$ 1,978
Other current assets
Restricted cash:
Restricted cash	3	2
Other deferred charges and assets
Restricted cash:
Restricted cash	21	0
SOUTHERN POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	192	182
Restricted cash:
Total cash, cash equivalents, and restricted cash	213	183	417	279
SOUTHERN POWER CO \| Other current assets
Restricted cash:
Restricted cash	0
SOUTHERN POWER CO \| Other deferred charges and assets
Restricted cash:
Restricted cash	21
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	29	17
Restricted cash:
Total cash, cash equivalents, and restricted cash	32	19	$ 161	$ 49
SOUTHERN Co GAS \| Other current assets
Restricted cash:
Restricted cash	3	2
SOUTHERN Co GAS \| Other deferred charges and assets
Restricted cash:
Restricted cash	$ 0	$ 0

Introduction - Asset Retirement

Introduction - Asset Retirement Obligations (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Aug. 31, 2021	Sep. 30, 2021
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		$ 10,684
Liabilities incurred		17
Liabilities settled		(341)
Accretion		304
Cash flow revisions		945
Ending balance		11,609
ALABAMA POWER CO
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		3,974
Liabilities incurred		0
Liabilities settled		(152)
Accretion		116
Cash flow revisions	$ 385	385
Ending balance		4,323
GEORGIA POWER CO
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		6,265
Liabilities incurred		3
Liabilities settled		(154)
Accretion		176
Cash flow revisions	435	475
Ending balance		6,765
MISSISSIPPI POWER CO
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		176
Liabilities incurred		0
Liabilities settled		(18)
Accretion		6
Cash flow revisions	$ 30	30
Ending balance		$ 194

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 432	$ 0
ALABAMA POWER CO \| Other regulatory liabilities, current
Loss Contingencies [Line Items]
Rate CNP Compliance	0	28
Retail Energy Cost Recovery	0	18
ALABAMA POWER CO \| Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Rate CNP Compliance	24	0
Natural Disaster Reserve	36	77
ALABAMA POWER CO \| Other regulatory assets, deferred
Loss Contingencies [Line Items]
Rate CNP PPA	88	58
Retail Energy Cost Recovery	6	0
ALABAMA POWER CO \| Other regulatory assets, current
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	79	0
GEORGIA POWER CO \| Over recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery	0	113
GEORGIA POWER CO \| Other deferred charges and assets
Loss Contingencies [Line Items]
Fuel Cost Recovery	203	0
MISSISSIPPI POWER CO \| Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Property Damage Reserve	0	4
MISSISSIPPI POWER CO \| Other regulatory assets, deferred
Loss Contingencies [Line Items]
Ad Valorem Tax	39	41
Property Damage Reserve	16	0
MISSISSIPPI POWER CO \| Other regulatory assets, current
Loss Contingencies [Line Items]
Ad Valorem Tax	12	11
MISSISSIPPI POWER CO \| Over recovered regulatory clause liabilities
Loss Contingencies [Line Items]
Fuel Cost Recovery	5	24
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Natural gas cost under recovery	432	0
SOUTHERN Co GAS \| Other regulatory liabilities
Loss Contingencies [Line Items]
Natural gas cost under recovery	0	88
SOUTHERN Co GAS \| Other regulatory assets, deferred
Loss Contingencies [Line Items]
Natural gas cost under recovery	79	0
SOUTHERN Co GAS \| Other regulatory assets, current
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 432	$ 0

Regulatory Matters - APC (Detai

Regulatory Matters - APC (Details)	3 Months Ended	9 Months Ended
Regulatory Matters - APC (Details)	Dec. 31, 2021USD ($)	Sep. 30, 2022USD ($)	Sep. 30, 2021USD ($)	Sep. 23, 2021MW	Apr. 15, 2021	Dec. 31, 2020USD ($)
Public Utilities, General Disclosures [Line Items]
Construction work in progress			$ 9,611,000,000			$ 8,697,000,000
ALABAMA POWER CO
Public Utilities, General Disclosures [Line Items]
Construction work in progress			1,129,000,000			866,000,000
Minimum natural disaster reserve balance, triggering establishment charge			50,000,000
Natural disaster reserve authorized limit			75,000,000
Natural disaster reserve balance			36,000,000
Natural disaster reserve, expected annual recovery until reserve is restored			16,000,000
ALABAMA POWER CO \| Calhoun Power Company, LLC
Public Utilities, General Disclosures [Line Items]
Approximate nameplate capacity (in MWs) \| MW				743
ALABAMA POWER CO \| Scenario, Forecast \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Natural disaster reserve, expected recovery amount	$ 4,000,000
ALABAMA POWER CO \| Scenario, Forecast \| Calhoun Power Company, LLC
Public Utilities, General Disclosures [Line Items]
Purchase price		$ 180,000,000
ALABAMA POWER CO \| Plant Barry Unit 8
Public Utilities, General Disclosures [Line Items]
Construction work in progress			222,000,000
MISSISSIPPI POWER CO
Public Utilities, General Disclosures [Line Items]
Construction work in progress			$ 117,000,000			$ 146,000,000
MISSISSIPPI POWER CO \| Plant Greene County Units 1 and 2 \| ALABAMA POWER CO
Public Utilities, General Disclosures [Line Items]
Proportionate ownership share					40.00%

Regulatory Matters - GPC Rate P

Regulatory Matters - GPC Rate Plan (Details) - GEORGIA POWER CO - USD ($) $ in Millions	Oct. 12, 2021	Oct. 01, 2021	Jan. 01, 2021
Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease) amount	$ 252
Traditional Base \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease) amount		$ 192
Environmental Compliance Cost Recovery \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease) amount		(12)
Demand-Side Management \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease) amount		(25)
Municipal Franchise Fee \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease) amount		$ 2
Plant Vogtle Units 3 And 4
Public Utilities, General Disclosures [Line Items]
Approved reduction in amortization of CCR ARO costs			$ 90

Regulatory Matters - GPC Plant

Regulatory Matters - GPC Plant Vogtle Units 3 and Common Facilities Rate Proceeding (Details) - GEORGIA POWER CO - USD ($) $ in Millions	Nov. 02, 2021	Oct. 12, 2021	Jun. 15, 2021
Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease) amount		$ 252
Plant Vogtle Unit 3
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease) amount			$ 2,380
Requested rate increase, annual amount			$ 302
Plant Vogtle Unit 3 \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease)	$ 2,100
Approved depreciation expense deferred, annual amount	$ 38

Regulatory Matters - GPC Deferr

Regulatory Matters - GPC Deferral of Incremental COVID-19 Costs (Details) - GEORGIA POWER CO $ in Millions	4 Months Ended
	Sep. 30, 2021USD ($)
Public Utilities, General Disclosures [Line Items]
Decrease in incremental COVID-19 costs deferred	$ 23
Incremental COVID-19 costs deferred	20
Incremental COVID-19 costs deferred, bad debt costs	1
Incremental COVID-19 costs deferred, other	$ 19

Regulatory Matters - GPC Fuel C

Regulatory Matters - GPC Fuel Cost Recovery (Details) - GEORGIA POWER CO - Subsequent Event $ in Millions	Oct. 12, 2021USD ($)
Public Utilities, General Disclosures [Line Items]
Requested revenues increase (decrease) percentage	15.00%
Requested rate increase (decrease) amount	$ 252

Regulatory Matters - GPC Nuclea

Regulatory Matters - GPC Nuclear Construction (Details) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2012utilityMW	Aug. 31, 2018
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	$ 264			$ 0	$ 772	$ 149
GEORGIA POWER CO
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	264	$ 460	$ 48	$ 0	772	149
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	$ 197	343	36		$ 576	$ 111
GEORGIA POWER CO \| Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Proportionate ownership share	45.70%				45.70%
Number of construction units approved \| utility							2
Electric generating capacity in mega watts under consortium agreement \| MW							1,100
Estimated cost to complete, construction contingency estimate, financing costs	$ 3,200				$ 3,200
Estimated cost to complete, construction contingency estimate, financing costs, incurred to date	2,800				2,800
Construction contingency estimate	127	341	84		127
Construction contingency estimate, additional amount	137	$ 119	$ 48		137
Base project capital cost forecast, monthly					25
Monthly AFUDC					$ 15
Percentage of ownership interest required for voting for continuing construction								90.00%
GEORGIA POWER CO \| Plant Vogtle Units 3 And 4 \| Vogtle Owners
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed					30 days
Minimum \| GEORGIA POWER CO \| Plant Vogtle Units 3 And 4 \| COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term					3 months
Estimate of possible loss	160				$ 160
Maximum \| GEORGIA POWER CO \| Plant Vogtle Units 3 And 4 \| COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term					4 months
Estimate of possible loss	$ 200				$ 200

Regulatory Matters - GPC Nucl_2

Regulatory Matters - GPC Nuclear Construction Cost and Schedule (Details) - GEORGIA POWER CO - Plant Vogtle Units 3 And 4 $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Loss Contingencies [Line Items]
Base project capital cost forecast	$ 9,342
Construction contingency estimate	137
Total project capital cost forecast	9,479
Net investment as of end of the period	(8,159)
Remaining estimate to complete	1,320
Estimated cost to complete, costs not shared with other owners	570
Expected capitalized costs	318
Capitalized interest accrued	169
Twenty Fourth Vogtle Construction Monitoring Report
Loss Contingencies [Line Items]
Guarantor obligations	1,700
Customer refund	$ 188

Regulatory Matters - GPC Amendm

Regulatory Matters - GPC Amendments to the Vogtle Joint Ownership Agreements (Details) - Plant Vogtle Units 3 And 4 - Georgia Power - USD ($) $ in Millions	Jan. 11, 2018	Sep. 30, 2021	Aug. 31, 2018
Public Utilities, General Disclosures [Line Items]
Production tax credits, aggregate purchase price, maximum		$ 300
Preliminary estimated cost to complete		9,479
Additional construction capital costs	$ 3,300	$ 350
Remaining share of construction costs, agreement to pay, percentage		100.00%
Percentage of ownership interest required for voting for continuing construction			90.00%
Percentage of costs, disallowed for recovery		6.00%
Costs disallowed for recovery, period		6 months
Public utilities, extension project schedule, term		1 year
Estimated cost to complete, starting dollar amount		$ 18,380
Category I
Public Utilities, General Disclosures [Line Items]
Preliminary estimated cost to complete		8,400
Additional construction capital costs, threshold		$ 800
Category II
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		55.70%
Additional construction capital costs		$ 80
Category II \| Vogtle Owners
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		44.30%
Category II \| Minimum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold		$ 800
Category II \| Maximum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold		$ 1,600
Category III
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		65.70%
Additional construction capital costs		$ 100
Category III \| Vogtle Owners
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		34.30%
Category III \| Minimum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold		$ 1,600
Category III \| Maximum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold		$ 2,100

Regulatory Matters - GPC Nucl_3

Regulatory Matters - GPC Nuclear Construction Regulatory Matters (Details) - Plant Vogtle Units 3 And 4 - Georgia Power $ in Millions

Oct. 01, 2021USD ($)

Jan. 01, 2021

Jan. 01, 2020

Jan. 11, 2018USD ($)

Jan. 01, 2016

Jun. 30, 2020USD ($)

Sep. 30, 2021USD ($)

Dec. 31, 2023USD ($)

Dec. 31, 2022USD ($)

Dec. 31, 2021USD ($)

Dec. 31, 2020USD ($)report

Dec. 31, 2009USD ($)

Jun. 30, 2018USD ($)

Dec. 31, 2013

Public Utilities, General Disclosures [Line Items]

Estimated in-service capital cost

$ 4,418

Financing costs collected, net of tax

$ 2,700

Additional construction capital costs

$ 3,300

$ 350

Payments for contractor settlement agreement

300

Amendment to estimated in-service capital cost

$ 5,680

Retail rate of return on common equity

10.95%

Public utilities, approved return on equity percentage

5.30%

8.30%

10.00%

Public utilities, approved return on equity, monthly percentage decrease

0.10%

Return on equity reduction, negative impact on earnings

$ 150

Increase to base capital cost forecast not seeking recovery

$ 700

Subsequent Event

Public Utilities, General Disclosures [Line Items]

Requested decrease in tariff

$ 78

Twenty Fourth Vogtle Construction Monitoring Report

Public Utilities, General Disclosures [Line Items]

Number of approved construction management reports | report

Requested capital construction costs

$ 9,200

$ 7,300

Guarantor obligations

$ 1,700

Customer refund

188

Twenty Fifth Vogtle Construction Monitoring Report

Public Utilities, General Disclosures [Line Items]

Cost settlement agreement revised forecast, net of payments

$ 7,300

Scenario, Forecast

Public Utilities, General Disclosures [Line Items]

Return on equity reduction, negative impact on earnings

$ 135

$ 260

$ 270

Regulatory Matters - MPC (Detai

Regulatory Matters - MPC (Details) - MISSISSIPPI POWER CO $ in Millions	Oct. 25, 2021USD ($)	Jun. 08, 2021USD ($)	Apr. 06, 2021USD ($)	Sep. 30, 2021USD ($)	Apr. 15, 2021MW	Dec. 31, 2020MW
Loss Contingencies [Line Items]
Approved rate increase (decrease)		$ 16	$ 28
Approved rate increase, percentage		1.80%
Required fossil-stream generation retirements (in MWs) \| MW						950
Public utilities, valorem taxes previously recovered, amount			$ 19
Hurricanes Zeta and Ida Accounting Order
Loss Contingencies [Line Items]
Retail costs to be reclassified to a regulatory asset due to accounting order				$ 49
Subsequent Event
Loss Contingencies [Line Items]
Requested rate increase (decrease) amount	$ 9
Environmental Compliance Overview Plan
Loss Contingencies [Line Items]
Approved rate increase (decrease)		$ 9
Plant Watson Unit 4
Loss Contingencies [Line Items]
Required fossil-stream generation retirements (in MWs) \| MW					268
Plant Greene County Units 1 and 2
Loss Contingencies [Line Items]
Required fossil-stream generation retirements (in MWs) \| MW					103
Plant Greene County Units 1 and 2 \| ALABAMA POWER CO
Loss Contingencies [Line Items]
Proportionate ownership share					40.00%
Plant Daniel Units 1 and 2
Loss Contingencies [Line Items]
Required fossil-stream generation retirements (in MWs) \| MW					502
Proportionate ownership share					50.00%
Remaining net book value				520
Estimated amount remaining at retirement				$ 390

Regulatory Matters - GAS Schedu

Regulatory Matters - GAS Schedule of Infrastructure Replacement Programs and Capital Projects (Details) - SOUTHERN Co GAS $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 343
Investing in Illinois
Public Utilities, General Disclosures [Line Items]
Capital expenditures	307
Steps to Advance Virginia's Energy
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 36

Regulatory Matters - GAS Narrat

Regulatory Matters - GAS Narrative (Details) $ in Millions	Oct. 14, 2021USD ($)	Sep. 14, 2021USD ($)	Jul. 21, 2021USD ($)	Apr. 28, 2021USD ($)	Nov. 01, 2020USD ($)	Apr. 06, 2021mi
Atlanta Gas Light
Loss Contingencies [Line Items]
Integrated capacity delivery plan, capital budgets and related operations and maintenance spending, term				10 years
Approved rate increase (decrease)			$ 49
Atlanta Gas Light \| Minimum
Loss Contingencies [Line Items]
Integrated capacity delivery plan, capital forecast plan, amount, years one through ten				$ 500
Atlanta Gas Light \| Maximum
Loss Contingencies [Line Items]
Integrated capacity delivery plan, capital forecast plan, amount, years one through ten				$ 600
Atlanta Gas Light \| Subsequent Event
Loss Contingencies [Line Items]
Requested revenues increase (decrease) percentage	(10.00%)
Requested rate increase (decrease) amount	$ 5
Integrated capacity delivery plan, capital forecast plan, amount, years one through three	$ 1,700
Virginia Natural Gas
Loss Contingencies [Line Items]
Requested rate increase (decrease) amount					$ 50
Motion filed to withdraw project application, header improvement project, scope of project (in miles) \| mi						9.5
Approved rate increase (decrease)		$ 43
Public utilities, approved rate increase amount recovery of investments		$ 14
Public utilities, approved return on equity percentage		9.50%
Public utilities, approved equity capital structure percentage		51.90%

Contingencies - General Litigat

Contingencies - General Litigation Matters (Details) - Pending Litigation $ in Millions	Oct. 08, 2021claim	Mar. 31, 2019plaintiff	Dec. 31, 2018USD ($)plaintiffdefendant	Dec. 31, 2017claim
Shareholder Derivative Lawsuits
Loss Contingencies [Line Items]
Pending number of claims				2
Stay period			30 days
GEORGIA POWER CO \| Subsequent Event
Loss Contingencies [Line Items]
Complaints filed	3
MISSISSIPPI POWER CO \| Purported Violations of Mississippi Consumer Protection Act
Loss Contingencies [Line Items]
Number of plaintiffs \| plaintiff		4	10
Number of defendants \| defendant			3
Underpayment of refunds \| $			$ 23.5

Contingencies - Environmental R

Contingencies - Environmental Remediation (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 19	$ 15
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 255	$ 245

Contingencies - Other Matters (

Contingencies - Other Matters (Details) $ in Millions	3 Months Ended			6 Months Ended		9 Months Ended
Contingencies - Other Matters (Details) $ in Millions	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Jan. 30, 2020mi
Loss Contingencies [Line Items]
Tax expense	$ 372		$ 293			$ 550	$ 443
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Asset impairment charges						84	0
Tax expense	133		$ 3			224	$ 98
SOUTHERN Co GAS \| PennEast Pipeline
Loss Contingencies [Line Items]
Construction amendment, number of miles of pipe, phase one \| mi								68
Construction amendment, number of miles of pipe, phase two \| mi								50
Asset impairment charges	2			$ 84	$ 82	84
Asset impairment charges, net of tax	$ 2	$ 67		$ 67	$ 58
Tax expense						$ 7
Ownership percentage, equity method investment	20.00%			20.00%		20.00%
SOUTHERN Co GAS \| SNG
Loss Contingencies [Line Items]
Ownership percentage, equity method investment	50.00%			50.00%		50.00%
Commitment to fund contingent capital contribution	$ 150			$ 150		$ 150
SNG
Loss Contingencies [Line Items]
Debt maturing in June 2021	$ 300			$ 300		$ 300

Revenue from Contracts with C_3

Revenue from Contracts with Customers and Lease Income - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 5,732	$ 5,755	$ 18,066	$ 15,771
Total operating revenues	6,238	5,620	17,346	15,258
Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4,332	4,178	11,006	10,540
Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,974	2,019	4,910	4,802
Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,432	1,354	3,727	3,589
Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	902	783	2,299	2,081
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	24	22	70	68
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	549	474	2,432	2,058
Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	218	170	1,143	906
Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	55	41	298	229
Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	239	224	775	723
Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6	4	29	21
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	31	35	187	179
Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	547	409	1,338	1,048
PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	359	214	782	550
PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	125	136	375	339
Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	63	59	181	159
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	56	476	2,498	1,448
Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers		431	2,168	1,168
Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	45	38	303	258
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	11	7	27	22
Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	248	218	792	677
Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	506	968	2,979	2,604
Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues		(1,103)	(3,699)	(3,117)
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,801	1,671	4,708	4,285
Total operating revenues	1,904	1,729	5,019	4,445
ALABAMA POWER CO \| Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,619	1,562	4,221	3,963
ALABAMA POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	750	752	1,931	1,839
ALABAMA POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	471	447	1,229	1,152
ALABAMA POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	394	358	1,048	956
ALABAMA POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4	5	13	16
ALABAMA POWER CO \| Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	129	76	337	205
ALABAMA POWER CO \| PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	61	40	143	94
ALABAMA POWER CO \| PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	14	26	86	78
ALABAMA POWER CO \| Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	54	10	108	33
ALABAMA POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers		0	0	0
ALABAMA POWER CO \| Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
ALABAMA POWER CO \| Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	53	33	150	117
ALABAMA POWER CO \| Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	103	58	311	160
ALABAMA POWER CO \| Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues		0	0	0
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,636	2,529	6,631	6,359
Total operating revenues	2,856	2,617	7,050	6,371
GEORGIA POWER CO \| Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,466	2,383	6,143	5,955
GEORGIA POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,138	1,183	2,765	2,760
GEORGIA POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	882	833	2,293	2,242
GEORGIA POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	428	352	1,034	907
GEORGIA POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	18	15	51	46
GEORGIA POWER CO \| Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	58	31	126	75
GEORGIA POWER CO \| PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	41	13	71	38
GEORGIA POWER CO \| PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	14	15	41	30
GEORGIA POWER CO \| Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3	3	14	7
GEORGIA POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers		0	0	0
GEORGIA POWER CO \| Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
GEORGIA POWER CO \| Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	112	115	362	329
GEORGIA POWER CO \| Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	220	88	419	12
GEORGIA POWER CO \| Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues		0	0	0
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	378	335	960	886
Total operating revenues	378	336	988	895
MISSISSIPPI POWER CO \| Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	247	233	642	622
MISSISSIPPI POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	86	84	214	203
MISSISSIPPI POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	79	74	205	195
MISSISSIPPI POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	80	73	217	218
MISSISSIPPI POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	2	6	6
MISSISSIPPI POWER CO \| Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	123	96	296	245
MISSISSIPPI POWER CO \| PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	2	9	7
MISSISSIPPI POWER CO \| PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1	1	4	3
MISSISSIPPI POWER CO \| Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	120	93	283	235
MISSISSIPPI POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers		0	0	0
MISSISSIPPI POWER CO \| Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
MISSISSIPPI POWER CO \| Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	8	6	22	19
MISSISSIPPI POWER CO \| Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	0	1	28	9
MISSISSIPPI POWER CO \| Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues		0	0	0
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	501	332	1,113	851
Total operating revenues	679	523	1,610	1,337
SOUTHERN POWER CO \| Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	492	328	1,095	840
SOUTHERN POWER CO \| PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	261	165	575	425
SOUTHERN POWER CO \| PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	97	95	247	231
SOUTHERN POWER CO \| Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	134	68	273	184
SOUTHERN POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers		0	0	0
SOUTHERN POWER CO \| Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN POWER CO \| Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	9	4	18	11
SOUTHERN POWER CO \| Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	178	191	497	486
SOUTHERN POWER CO \| Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues		0	0	0
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	605	950	4,930	3,506
Total operating revenues	623	477	2,994	2,362
SOUTHERN Co GAS \| Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	549	474	2,432	2,058
SOUTHERN Co GAS \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	218	170	1,143	906
SOUTHERN Co GAS \| Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	55	41	298	229
SOUTHERN Co GAS \| Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	239	224	775	723
SOUTHERN Co GAS \| Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6	4	29	21
SOUTHERN Co GAS \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	31	35	187	179
SOUTHERN Co GAS \| Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	56	476	2,498	1,448
SOUTHERN Co GAS \| Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers		431	2,168	1,168
SOUTHERN Co GAS \| Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	45	38	303	258
SOUTHERN Co GAS \| Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	11	7	27	22
SOUTHERN Co GAS \| Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
SOUTHERN Co GAS \| Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	$ 18	630	1,763	1,973
SOUTHERN Co GAS \| Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues		$ (1,103)	$ (3,699)	$ (3,117)

Revenue from Contracts with C_4

Revenue from Contracts with Customers and Lease Income - Schedule of Contract Balances (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Accounts Receivable	$ 2,343	$ 2,614
Contract Assets	165	158
Contract Liabilities	65	61
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	712	632
Contract Assets	5	2
Contract Liabilities	6	6
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	904	806
Contract Assets	103	71
Contract Liabilities	39	27
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	90	77
Contract Assets	0	0
Contract Liabilities	1	1
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	170	112
Contract Assets	1	0
Contract Liabilities	2	1
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Accounts Receivable	329	788
Contract Assets	0	0
Contract Liabilities	$ 0	$ 1

Revenue from Contracts with C_5

Revenue from Contracts with Customers and Lease Income - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Contract assets	$ 165		$ 165		$ 158
Contract liabilities	65		65		61
Revenue from contracts with customers recognized	5		25
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract assets	55		55		81
Contract liabilities	19		19		27
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Contract assets	0		0		0
Contract liabilities	1		1		1
Sales-type lease, lease receivable	39		39
Transfer of construction work in progress to lease receivables	39
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Contract assets	1		1		0
Contract liabilities	2		2		1
Sales-type lease, lease receivable	113		113
Transfer of construction work in progress to lease receivables	113
Loss on sales-type lease	$ 15	$ 0	$ 15	$ 0
Lessor, lease term, sales-type lease	20 years		20 years
Net investment in sales-type lease, current portion	$ 8		$ 8
Net investment in sales-type lease, long-term portion	$ 91		$ 91		$ 0

Revenue from Contracts with C_6

Revenue from Contracts with Customers and Lease Income - Schedule of Remaining Performance Obligations (Details) $ in Millions	Sep. 30, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 156
Performance obligation, expected timing of satisfaction	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 543
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 347
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 327
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 307
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2,667
Performance obligation, expected timing of satisfaction
ALABAMA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 13
Performance obligation, expected timing of satisfaction	3 months
ALABAMA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 32
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 24
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 7
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 5
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction
GEORGIA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 22
Performance obligation, expected timing of satisfaction	3 months
GEORGIA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 64
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 43
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 23
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 21
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 41
Performance obligation, expected timing of satisfaction
SOUTHERN POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 70
Performance obligation, expected timing of satisfaction	3 months
SOUTHERN POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 323
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 281
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 297
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 281
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2,644
Performance obligation, expected timing of satisfaction

Revenue from Contracts with C_7

Revenue from Contracts with Customers and Lease Income - Schedule of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 4	$ 3	$ 11	$ 8
Lease income - operating leases	56	50	168	148
Variable lease income	143	145	355	345
Total lease income	203	198	534	501
ALABAMA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	21	11	62	24
Variable lease income	0	0	0	0
Total lease income	21	11	62	24
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	11	14	31	44
Variable lease income	0	0	0	0
Total lease income	11	14	31	44
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	4	3	10	8
Lease income - operating leases	0	0	1	1
Variable lease income	0	0	0	0
Total lease income	4	3	11	9
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	21	21	64	66
Variable lease income	151	153	379	368
Total lease income	172	174	443	434
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0	0	0
Lease income - operating leases	9	9	26	26
Variable lease income	0	0	0	0
Total lease income	$ 9	$ 9	$ 26	$ 26

Revenue from Contracts with C_8

Revenue from Contracts with Customers and Lease Income - Undiscounted Cash Flows to be Received Under Tolling Arrangements Accounted for as Sales-type Leases (Details) $ in Millions	Sep. 30, 2021USD ($)
Sales-type and Direct Financing Leases, Lease Receivable, Fiscal Year Maturity [Abstract]
2021 (remaining)	$ 2
SOUTHERN POWER CO
Sales-type and Direct Financing Leases, Lease Receivable, Fiscal Year Maturity [Abstract]
2022	8
2023	8
2024	8
2025	8
2026	8
Thereafter	115
Total undiscounted cash flows	157
Net investment in sales-type lease	99
Difference between undiscounted cash flows and discounted cash flows	$ 58

Consolidated Entities and Equ_3

Consolidated Entities and Equity Method Investments - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)investor	Dec. 31, 2020USD ($)
Schedule of Equity Method Investments [Line Items]
Assets	$ 127,861	$ 122,935
Liabilities	94,351	90,410
Equity investments in unconsolidated subsidiaries	1,278	1,362
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	13,611	13,235
Liabilities	6,904	6,604
Equity investments in unconsolidated subsidiaries	$ 83	19
SP Solar Holdings I, LP \| SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	67.00%
SP Solar Holdings I, LP \| Global Atlantic
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	33.00%
Variable Interest Entity, Primary Beneficiary \| SP Solar Holdings I, LP \| SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 6,200	6,100
Liabilities	364	387
Noncontrolling interests related to other partners' interests	1,100	1,100
Variable Interest Entity, Primary Beneficiary \| SP Wind \| SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	2,300	2,400
Liabilities	157	138
Noncontrolling interests related to other partners' interests	$ 42	43
Distribution made to limited partner, cash distributions paid, percentage	60.00%
Number of financial investors \| investor	3
Variable Interest Entity, Primary Beneficiary \| SP Wind \| Financial Investors
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	40.00%
Variable Interest Entity, Primary Beneficiary \| Other Variable Interest Entities \| SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 1,900	1,100
Liabilities	263	110
Noncontrolling interests related to other partners' interests	$ 902	$ 454

Consolidated Entities and Equ_4

Consolidated Entities and Equity Method Investments - Schedule of Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 1,278	$ 1,278		$ 1,278		$ 1,362
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,174	1,174		1,174		1,290
Asset impairment charges				84	$ 0
SOUTHERN Co GAS \| SNG
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,130	1,130		1,130		1,167
SOUTHERN Co GAS \| PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Investment Balance	11	11		11		91
Asset impairment charges	2	84	$ 82	84
SOUTHERN Co GAS \| Other
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 33	$ 33		$ 33		$ 32

Consolidated Entities and Equ_5

Consolidated Entities and Equity Method Investments - Schedule of Earnings (Loss) from Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	$ 30		$ 33			$ 35	$ 105
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	25		33			14	106
Asset impairment charges						84	0
SOUTHERN Co GAS \| SNG
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	27		30			93	95
SOUTHERN Co GAS \| PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	(2)		2			(81)	5
Asset impairment charges	2			$ 84	$ 82	84
Asset impairment charges, net of tax	2	$ 67		$ 67	$ 58
SOUTHERN Co GAS \| Other
Schedule of Equity Method Investments [Line Items]
Earnings (Loss) from Equity Method Investments	$ 0		$ 1			$ 2	$ 6

Financing - Schedule of Credit

Financing - Schedule of Credit Arrangements (Details) - USD ($)	Sep. 30, 2021	Aug. 31, 2021	Jul. 31, 2021	May 31, 2021	Apr. 30, 2021
Line of Credit Facility [Line Items]
Expires, 2022	$ 280,000,000
Expires, 2023	125,000,000
Expires, 2024	700,000,000
Expires, 2026	6,550,000,000
Total	7,655,000,000
Unused	7,570,000,000
Due within One Year	280,000,000
Southern Company parent
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	0
Expires, 2024	0
Expires, 2026	2,000,000,000
Total	2,000,000,000
Unused	1,999,000,000
Due within One Year	0
ALABAMA POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0		$ 525,000,000
Expires, 2023	0
Expires, 2024	550,000,000	$ 550,000,000
Expires, 2026	700,000,000
Total	1,250,000,000			$ 700,000,000	$ 800,000,000
Unused	1,250,000,000
Due within One Year	0
GEORGIA POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	0
Expires, 2024	0
Expires, 2026	1,750,000,000
Total	1,750,000,000
Unused	1,726,000,000
Due within One Year	0
MISSISSIPPI POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	125,000,000
Expires, 2024	150,000,000
Expires, 2026	0
Total	275,000,000			150,000,000
Unused	250,000,000
Due within One Year	0
SOUTHERN POWER CO
Line of Credit Facility [Line Items]
Expires, 2022	0
Expires, 2023	0
Expires, 2024	0
Expires, 2026	600,000,000
Total	600,000,000
Unused	568,000,000
Due within One Year	0
SOUTHERN POWER CO \| Continuing Letter of Credit Facility A
Line of Credit Facility [Line Items]
Expires, 2023	75,000,000
Unused	23,000,000
SOUTHERN POWER CO \| Continuing Letter of Credit Facility B
Line of Credit Facility [Line Items]
Expires, 2023	60,000,000
Unused	1,000,000
SOUTHERN Co GAS
Line of Credit Facility [Line Items]
Expires, 2022	250,000,000
Expires, 2023	0
Expires, 2024	0
Expires, 2026	1,500,000,000
Total	1,750,000,000			$ 1,500,000,000	$ 1,750,000,000
Unused	1,747,000,000
Due within One Year	250,000,000
SEGCO
Line of Credit Facility [Line Items]
Expires, 2022	30,000,000
Expires, 2023	0
Expires, 2024	0
Expires, 2026	0
Total	30,000,000
Unused	30,000,000
Due within One Year	30,000,000
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	800,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	$ 700,000,000

Financing - Narrative (Details)

Financing - Narrative (Details) - USD ($)	Sep. 30, 2021	Aug. 31, 2021	Jul. 31, 2021	May 31, 2021	Apr. 30, 2021
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 7,655,000,000
Line of credit expiring in 2022	280,000,000
Line of credit expiring in 2024	700,000,000
Variable rate pollution control revenue bonds outstanding	1,600,000,000
ALABAMA POWER CO
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	1,250,000,000			$ 700,000,000	$ 800,000,000
Line of credit expiring in 2022	0		$ 525,000,000
Line of credit expiring in 2024	550,000,000	$ 550,000,000
Variable rate pollution control revenue bonds outstanding	854,000,000
SOUTHERN Co GAS
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	1,750,000,000			1,500,000,000	$ 1,750,000,000
Line of credit expiring in 2022	250,000,000
Line of credit expiring in 2024	0
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	275,000,000			$ 150,000,000
Line of credit expiring in 2022	0
Line of credit expiring in 2024	150,000,000
Variable rate pollution control revenue bonds outstanding	34,000,000
Fixed rate pollution control revenue bonds outstanding	50,000,000
GEORGIA POWER CO
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	1,750,000,000
Line of credit expiring in 2022	0
Line of credit expiring in 2024	0
Variable rate pollution control revenue bonds outstanding	672,000,000
Fixed rate pollution control revenue bonds outstanding	$ 262,000,000

Financing - Schedule of Shares

Financing - Schedule of Shares Used to Compute Diluted Earnings Per Share (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Disclosure [Abstract]
As reported shares (in shares)	1,061	1,058	1,060	1,058
Effect of stock-based compensation (in shares)	7	6	7	6
Diluted shares (in shares)	1,068	1,064	1,067	1,064

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Billions	9 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Billions	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	17.50%	13.90%
ITC and PTC carryforwards
Income Tax Contingency [Line Items]
Deferred tax assets	$ 1.2		$ 1.4
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	7.30%	12.30%
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	(1.60%)	11.30%
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	36.60%	21.40%

Income Taxes - Summary of Opera

Income Taxes - Summary of Operating Loss Carryforwards Valuation Allowances (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 142	$ 112
GEORGIA POWER CO
Operating Loss Carryforwards [Line Items]
Valuation allowance	58	28
Federal
Operating Loss Carryforwards [Line Items]
Valuation allowance	20	20
Federal \| GEORGIA POWER CO
Operating Loss Carryforwards [Line Items]
Valuation allowance	0	0
State (net of federal benefit)
Operating Loss Carryforwards [Line Items]
Valuation allowance	122	92
State (net of federal benefit) \| GEORGIA POWER CO
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 58	$ 28

Retirement Benefits (Details)

Retirement Benefits (Details) - USD ($)	3 Months Ended		9 Months Ended
Retirement Benefits (Details) - USD ($)	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, remainder of fiscal year	$ 0		$ 0
Pension Plans and Postretirement Plans
Service cost	109,000,000	$ 94,000,000	326,000,000	$ 282,000,000
Interest cost	87,000,000	108,000,000	260,000,000	324,000,000
Expected return on plan assets	(298,000,000)	(274,000,000)	(893,000,000)	(824,000,000)
Amortization:
Prior service costs	0	0	0	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	78,000,000	67,000,000	235,000,000	201,000,000
Net periodic pension cost (income)	(24,000,000)	(5,000,000)	(72,000,000)	(16,000,000)
Pension Plans \| ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	26,000,000	23,000,000	77,000,000	67,000,000
Interest cost	20,000,000	25,000,000	61,000,000	75,000,000
Expected return on plan assets	(72,000,000)	(66,000,000)	(215,000,000)	(198,000,000)
Amortization:
Prior service costs	0	1,000,000	0	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	21,000,000	17,000,000	62,000,000	53,000,000
Net periodic pension cost (income)	(5,000,000)	0	(15,000,000)	(2,000,000)
Pension Plans \| GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	28,000,000	24,000,000	84,000,000	72,000,000
Interest cost	26,000,000	33,000,000	78,000,000	100,000,000
Expected return on plan assets	(94,000,000)	(87,000,000)	(282,000,000)	(261,000,000)
Amortization:
Prior service costs	0	0	1,000,000	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	25,000,000	22,000,000	75,000,000	65,000,000
Net periodic pension cost (income)	(15,000,000)	(8,000,000)	(44,000,000)	(23,000,000)
Pension Plans \| MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	3,000,000	13,000,000	11,000,000
Interest cost	4,000,000	5,000,000	12,000,000	15,000,000
Expected return on plan assets	(14,000,000)	(13,000,000)	(41,000,000)	(38,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	4,000,000	4,000,000	11,000,000	10,000,000
Net periodic pension cost (income)	(2,000,000)	(1,000,000)	(5,000,000)	(2,000,000)
Pension Plans \| SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000	7,000,000	6,000,000
Interest cost	2,000,000	1,000,000	4,000,000	4,000,000
Expected return on plan assets	(4,000,000)	(4,000,000)	(11,000,000)	(10,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	1,000,000	1,000,000	3,000,000	2,000,000
Net periodic pension cost (income)	1,000,000	0	3,000,000	2,000,000
Pension Plans \| SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	10,000,000	8,000,000	28,000,000	24,000,000
Interest cost	6,000,000	8,000,000	18,000,000	23,000,000
Expected return on plan assets	(21,000,000)	(20,000,000)	(64,000,000)	(59,000,000)
Amortization:
Prior service costs	(1,000,000)	(1,000,000)	(2,000,000)	(2,000,000)
Regulatory asset	3,000,000	4,000,000	11,000,000	12,000,000
Net (gain)/loss	3,000,000	2,000,000	9,000,000	7,000,000
Net periodic pension cost (income)	0	1,000,000	0	5,000,000
Postretirement Benefits
Pension Plans and Postretirement Plans
Service cost	6,000,000	6,000,000	18,000,000	17,000,000
Interest cost	9,000,000	13,000,000	26,000,000	40,000,000
Expected return on plan assets	(19,000,000)	(18,000,000)	(57,000,000)	(54,000,000)
Amortization:
Prior service costs		0	(1,000,000)	(1,000,000)
Regulatory asset	0	0	0	0
Net (gain)/loss	1,000,000	1,000,000	3,000,000	2,000,000
Net periodic pension cost (income)	(3,000,000)	2,000,000	(11,000,000)	4,000,000
Postretirement Benefits \| ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	1,000,000	5,000,000	4,000,000
Interest cost	2,000,000	4,000,000	6,000,000	10,000,000
Expected return on plan assets	(8,000,000)	(7,000,000)	(22,000,000)	(21,000,000)
Amortization:
Prior service costs		0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	(4,000,000)	(2,000,000)	(11,000,000)	(7,000,000)
Postretirement Benefits \| GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000	5,000,000	5,000,000
Interest cost	3,000,000	5,000,000	9,000,000	15,000,000
Expected return on plan assets	(7,000,000)	(7,000,000)	(20,000,000)	(20,000,000)
Amortization:
Prior service costs		(1,000,000)	0	(1,000,000)
Regulatory asset	0	0	0	0
Net (gain)/loss	1,000,000	1,000,000	2,000,000	2,000,000
Net periodic pension cost (income)	(1,000,000)	0	(4,000,000)	1,000,000
Postretirement Benefits \| MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	(1,000,000)	1,000,000	0
Interest cost	0	1,000,000	1,000,000	2,000,000
Expected return on plan assets	(1,000,000)	0	(2,000,000)	(1,000,000)
Amortization:
Prior service costs		0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	0	0	0	1,000,000
Postretirement Benefits \| SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	1,000,000	1,000,000
Interest cost	0	0	0	0
Expected return on plan assets	0	0	0	0
Amortization:
Prior service costs		0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	1,000,000	1,000,000	1,000,000	1,000,000
Postretirement Benefits \| SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	0	0	1,000,000	1,000,000
Interest cost	1,000,000	2,000,000	3,000,000	5,000,000
Expected return on plan assets	(2,000,000)	(2,000,000)	(6,000,000)	(5,000,000)
Amortization:
Prior service costs		0	0	0
Regulatory asset	2,000,000	2,000,000	5,000,000	5,000,000
Net (gain)/loss	(1,000,000)	(1,000,000)	(2,000,000)	(2,000,000)
Net periodic pension cost (income)	$ 0	$ 1,000,000	$ 1,000,000	$ 4,000,000

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets:
Derivatives	$ 489	$ 281
Liabilities:
Derivatives	66	64
Other	13
Collateral already posted, assets, aggregate fair value	(20)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities:
Other	0
Significant Other Observable Inputs (Level 2)
Liabilities:
Other	13
Significant Unobservable Inputs (Level 3)
Liabilities:
Other	0
ALABAMA POWER CO
Assets:
Derivatives	106	5
Liabilities:
Derivatives	1	0
GEORGIA POWER CO
Assets:
Derivatives	163	3
Investments in trusts	57
Liabilities:
Derivatives	1	1
MISSISSIPPI POWER CO
Assets:
Derivatives	103	2
Liabilities:
Derivatives	1	2
SOUTHERN POWER CO
Assets:
Derivatives	29	89
Liabilities:
Derivatives	12	26
Other	13
SOUTHERN POWER CO \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities:
Other	0
SOUTHERN POWER CO \| Significant Other Observable Inputs (Level 2)
Liabilities:
Other	13
SOUTHERN POWER CO \| Significant Unobservable Inputs (Level 3)
Liabilities:
Other	0
SOUTHERN Co GAS
Assets:
Derivatives	74	162
Liabilities:
Derivatives	7	35
Total
Collateral already posted, assets, aggregate fair value	(20)	$ 28
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	1,507
Other investments	35
Total	4,562
Liabilities:
Contingent consideration	16
Total	132
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	1,498
Other investments	9
Total	2,523
Liabilities:
Contingent consideration	0
Total	27
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	9
Other investments	26
Total	1,916
Liabilities:
Contingent consideration	0
Total	89
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Other investments	0
Total	0
Liabilities:
Contingent consideration	16
Total	16
Fair Value, Measurements, Recurring \| Net Asset Value as a Practical Expedient (NAV)
Assets:
Total	123
Fair Value, Measurements, Recurring \| Energy-related derivatives
Assets:
Derivatives	500
Liabilities:
Derivatives	44
Fair Value, Measurements, Recurring \| Energy-related derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	75
Liabilities:
Derivatives	27
Fair Value, Measurements, Recurring \| Energy-related derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	425
Liabilities:
Derivatives	17
Fair Value, Measurements, Recurring \| Energy-related derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| Interest rate derivatives
Assets:
Derivatives	25
Liabilities:
Derivatives	16
Fair Value, Measurements, Recurring \| Interest rate derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| Interest rate derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	25
Liabilities:
Derivatives	16
Fair Value, Measurements, Recurring \| Interest rate derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| Foreign currency derivatives
Assets:
Derivatives	20
Liabilities:
Derivatives	43
Fair Value, Measurements, Recurring \| Foreign currency derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| Foreign currency derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	20
Liabilities:
Derivatives	43
Fair Value, Measurements, Recurring \| Foreign currency derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| Domestic equity
Assets:
Investments in trusts	975
Fair Value, Measurements, Recurring \| Domestic equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	738
Fair Value, Measurements, Recurring \| Domestic equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	237
Fair Value, Measurements, Recurring \| Domestic equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Foreign equity
Assets:
Investments in trusts	350
Fair Value, Measurements, Recurring \| Foreign equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	167
Fair Value, Measurements, Recurring \| Foreign equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	183
Fair Value, Measurements, Recurring \| Foreign equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| U.S. Treasury and government agency securities
Assets:
Investments in trusts	352
Fair Value, Measurements, Recurring \| U.S. Treasury and government agency securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| U.S. Treasury and government agency securities \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	352
Fair Value, Measurements, Recurring \| U.S. Treasury and government agency securities \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Municipal bonds
Assets:
Investments in trusts	48
Fair Value, Measurements, Recurring \| Municipal bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Municipal bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	48
Fair Value, Measurements, Recurring \| Municipal bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Pooled funds – fixed income
Assets:
Investments in trusts	14
Fair Value, Measurements, Recurring \| Pooled funds – fixed income \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Pooled funds – fixed income \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	14
Fair Value, Measurements, Recurring \| Pooled funds – fixed income \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Corporate bonds
Assets:
Investments in trusts	474
Fair Value, Measurements, Recurring \| Corporate bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	2
Fair Value, Measurements, Recurring \| Corporate bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	472
Fair Value, Measurements, Recurring \| Corporate bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Mortgage and asset backed securities
Assets:
Investments in trusts	92
Fair Value, Measurements, Recurring \| Mortgage and asset backed securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Mortgage and asset backed securities \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	92
Fair Value, Measurements, Recurring \| Mortgage and asset backed securities \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Private equity
Assets:
Investments in trusts	123
Fair Value, Measurements, Recurring \| Private equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Private equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Private equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Private equity \| Net Asset Value as a Practical Expedient (NAV)
Assets:
Investments in trusts	123
Fair Value, Measurements, Recurring \| Cash and cash equivalents
Assets:
Investments in trusts	5
Fair Value, Measurements, Recurring \| Cash and cash equivalents \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	5
Fair Value, Measurements, Recurring \| Cash and cash equivalents \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Cash and cash equivalents \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| Other
Assets:
Investments in trusts	42
Fair Value, Measurements, Recurring \| Other \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	29
Fair Value, Measurements, Recurring \| Other \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	13
Fair Value, Measurements, Recurring \| Other \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO
Assets:
Cash equivalents	452
Other investments	26
Total	1,844
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	443
Other investments	0
Total	1,062
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	9
Other investments	26
Total	659
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Other investments	0
Total	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Net Asset Value as a Practical Expedient (NAV)
Assets:
Total	123
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Energy-related derivatives
Assets:
Derivatives	104
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Energy-related derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Energy-related derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	104
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Energy-related derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Interest rate derivatives
Assets:
Derivatives	5
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Interest rate derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Interest rate derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	5
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Interest rate derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Domestic equity
Assets:
Investments in trusts	671
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Domestic equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	444
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Domestic equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	227
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Domestic equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Foreign equity
Assets:
Investments in trusts	167
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Foreign equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	167
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Foreign equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Foreign equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| U.S. Treasury and government agency securities
Assets:
Investments in trusts	22
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| U.S. Treasury and government agency securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| U.S. Treasury and government agency securities \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	22
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| U.S. Treasury and government agency securities \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Municipal bonds
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Municipal bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Municipal bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Municipal bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Corporate bonds
Assets:
Investments in trusts	245
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Corporate bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	2
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Corporate bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	243
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Corporate bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Mortgage and asset backed securities
Assets:
Investments in trusts	22
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Mortgage and asset backed securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Mortgage and asset backed securities \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	22
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Mortgage and asset backed securities \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Private equity
Assets:
Investments in trusts	123
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Private equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Private equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Private equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Private equity \| Net Asset Value as a Practical Expedient (NAV)
Assets:
Investments in trusts	123
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Other
Assets:
Investments in trusts	6
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Other \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	6
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Other \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| ALABAMA POWER CO \| Other \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO
Assets:
Cash equivalents	240
Total	1,593
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	240
Total	557
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Total	1,036
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Total	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Energy-related derivatives
Assets:
Derivatives	166
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Energy-related derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Energy-related derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	166
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Energy-related derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Domestic equity
Assets:
Investments in trusts	295
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Domestic equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	294
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Domestic equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Domestic equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Foreign equity
Assets:
Investments in trusts	180
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Foreign equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Foreign equity \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	180
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Foreign equity \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| U.S. Treasury and government agency securities
Assets:
Investments in trusts	330
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| U.S. Treasury and government agency securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| U.S. Treasury and government agency securities \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	330
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| U.S. Treasury and government agency securities \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Municipal bonds
Assets:
Investments in trusts	47
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Municipal bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Municipal bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	47
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Municipal bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Corporate bonds
Assets:
Investments in trusts	229
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Corporate bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Corporate bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	229
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Corporate bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Mortgage and asset backed securities
Assets:
Investments in trusts	70
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Mortgage and asset backed securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Mortgage and asset backed securities \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	70
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Mortgage and asset backed securities \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Other
Assets:
Investments in trusts	36
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Other \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	23
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Other \| Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	13
Fair Value, Measurements, Recurring \| GEORGIA POWER CO \| Other \| Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO
Assets:
Cash equivalents	121
Total	226
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	121
Total	121
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Total	105
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Total	0
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO \| Energy-related derivatives
Assets:
Derivatives	105
Liabilities:
Derivatives	3
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO \| Energy-related derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO \| Energy-related derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	105
Liabilities:
Derivatives	3
Fair Value, Measurements, Recurring \| MISSISSIPPI POWER CO \| Energy-related derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO
Assets:
Total	30
Liabilities:
Contingent consideration	16
Total	42
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	0
Liabilities:
Contingent consideration	0
Total	0
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Significant Other Observable Inputs (Level 2)
Assets:
Total	30
Liabilities:
Contingent consideration	0
Total	26
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Significant Unobservable Inputs (Level 3)
Assets:
Total	0
Liabilities:
Contingent consideration	16
Total	16
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Energy-related derivatives
Assets:
Derivatives	10
Liabilities:
Derivatives	2
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Energy-related derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Energy-related derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	10
Liabilities:
Derivatives	2
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Energy-related derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Foreign currency derivatives
Assets:
Derivatives	20
Liabilities:
Derivatives	11
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Foreign currency derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Foreign currency derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	20
Liabilities:
Derivatives	11
Fair Value, Measurements, Recurring \| SOUTHERN POWER CO \| Foreign currency derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS
Assets:
Total	152
Liabilities:
Total	35
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	80
Liabilities:
Total	27
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Significant Other Observable Inputs (Level 2)
Assets:
Total	72
Liabilities:
Total	8
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Significant Unobservable Inputs (Level 3)
Assets:
Total	0
Liabilities:
Total	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Energy-related derivatives
Assets:
Derivatives	115
Liabilities:
Derivatives	31
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Energy-related derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	75
Liabilities:
Derivatives	27
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Energy-related derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	40
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Energy-related derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Interest rate derivatives
Assets:
Derivatives	6
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Interest rate derivatives \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Interest rate derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	6
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Interest rate derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Domestic equity
Assets:
Non-qualified deferred compensation trusts	9
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Domestic equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Domestic equity \| Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	9
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Domestic equity \| Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Foreign equity
Assets:
Non-qualified deferred compensation trusts	3
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Foreign equity \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Foreign equity \| Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	3
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Foreign equity \| Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Pooled funds – fixed income
Assets:
Non-qualified deferred compensation trusts	14
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Pooled funds – fixed income \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Pooled funds – fixed income \| Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	14
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Pooled funds – fixed income \| Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Cash equivalents
Assets:
Non-qualified deferred compensation trusts	5
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Cash equivalents \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	5
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Cash equivalents \| Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring \| SOUTHERN Co GAS \| Cash equivalents \| Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	$ 0

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Increase (Decrease) In Fair Value Of Funds (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 9	$ 108	$ 173	$ 85
ALABAMA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	15	66	133	24
GEORGIA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ (6)	$ 42	$ 40	$ 61

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - ALABAMA POWER CO - Private equity $ in Millions	Sep. 30, 2021USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value	$ 123
Unfunded commitments	$ 72

Fair Value Measurements - Sch_3

Fair Value Measurements - Schedule of Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Sep. 30, 2021USD ($)
Long-term debt, including securities due within one year:
Carrying amount	$ 51,900
Fair value	57,600
ALABAMA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	9,100
Fair value	10,400
GEORGIA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	13,600
Fair value	15,200
MISSISSIPPI POWER CO
Long-term debt, including securities due within one year:
Carrying amount	1,600
Fair value	1,700
SOUTHERN POWER CO
Long-term debt, including securities due within one year:
Carrying amount	4,000
Fair value	4,400
SOUTHERN Co GAS
Long-term debt, including securities due within one year:
Carrying amount	6,800
Fair value	$ 7,800

Fair Value Measurements - Sch_4

Fair Value Measurements - Schedule of Fair Value of Commodity Derivative Contracts that Include a Significant Unobservable Component (Details) - SOUTHERN Co GAS - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 18	$ 28
Instruments realized or otherwise settled during period	0	(6)
Changes in fair value	0	(4)
Sale of Sequent	(18)	(18)
Ending balance	$ 0	$ 0

Derivatives - Schedule of Energ

Derivatives - Schedule of Energy-Related Derivatives (Details) - Energy-related, Natural Gas MMBTU in Millions	Sep. 30, 2021MMBTU
Energy-related derivative contracts
Net Purchased mmBtu	336
ALABAMA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	75
GEORGIA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	99
MISSISSIPPI POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	79
SOUTHERN POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	6
SOUTHERN Co GAS
Energy-related derivative contracts
Net Purchased mmBtu	77
SOUTHERN Co GAS \| Derivatives not designated as hedging instruments \| Long
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	91.4
SOUTHERN Co GAS \| Derivatives not designated as hedging instruments \| Short
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	14.3

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) MMBTU in Millions	9 Months Ended
Derivatives - Narrative (Details) MMBTU in Millions	Sep. 30, 2021USD ($)MMBTU	Dec. 31, 2020USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints \| MMBTU	41
Cash flow hedge gain (loss) to be reclassified within twelve months \| $	$ (22,000,000)
Collateral already posted, assets, aggregate fair value \| $	$ (20,000,000)
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints \| MMBTU	10
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints \| MMBTU	13
MISSISSIPPI POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints \| MMBTU	5
SOUTHERN POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints \| MMBTU	13
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months \| $	$ (4,000,000)
Registrants \| Derivative Counterparties
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value \| $	0
SOUTHERN Co GAS
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value \| $	$ (20,000,000)	$ 28,000,000

Derivatives - Schedule of Inter

Derivatives - Schedule of Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Derivative [Line Items]
Notional Amount	$ 2,050
Fair Value Gain (Loss) at September 30, 2021	$ 8
ALABAMA POWER CO \| Fair Value Hedges of Existing Debt
Derivative [Line Items]
Weighted Average Interest Rate Paid	1.91%
ALABAMA POWER CO \| Fair Value Hedges of Existing Debt \| March 2028
Derivative [Line Items]
Notional Amount	$ 150
Interest Rate Received	0.00%
Fair Value Gain (Loss) at September 30, 2021	$ 5
Southern Company parent \| Fair Value Hedges of Existing Debt \| March 2028
Derivative [Line Items]
Notional Amount	$ 400
Interest Rate Received	1.75%
Fair Value Gain (Loss) at September 30, 2021	$ (2)
Southern Company parent \| Fair Value Hedges of Existing Debt \| April 2030
Derivative [Line Items]
Notional Amount	$ 1,000
Interest Rate Received	3.70%
Fair Value Gain (Loss) at September 30, 2021	$ 3
SOUTHERN Co GAS \| Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 500
Interest Rate Received	1.75%
Fair Value Gain (Loss) at September 30, 2021	$ 2
London Interbank Offered Rate (LIBOR) \| Southern Company parent \| Fair Value Hedges of Existing Debt \| March 2028
Derivative [Line Items]
Weighted Average Interest Rate Paid	0.68%
London Interbank Offered Rate (LIBOR) \| Southern Company parent \| Fair Value Hedges of Existing Debt \| April 2030
Derivative [Line Items]
Weighted Average Interest Rate Paid	2.36%
London Interbank Offered Rate (LIBOR) \| SOUTHERN Co GAS \| Fair Value Hedges of Existing Debt
Derivative [Line Items]
Weighted Average Interest Rate Paid	0.38%

Derivatives - Schedule of Forei

Derivatives - Schedule of Foreign Currency Derivatives (Details) - 9 months ended Sep. 30, 2021 - Foreign currency derivatives € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Pay Notional	$ 2,717
Receive Notional \| €		€ 2,350
Fair Value Gain (Loss) at September 30, 2021	(23)
Fair Value Hedges of Existing Debt \| Southern Company parent
Derivative [Line Items]
Pay Notional	$ 1,476
Pay Rate	3.39%
Receive Notional \| €		1,250
Receive Rate	1.88%
Fair Value Gain (Loss) at September 30, 2021	$ (32)
Cash Flow Hedges of Existing Debt \| SOUTHERN POWER CO
Derivative [Line Items]
Pay Notional	1,241
Receive Notional \| €		1,100
Fair Value Gain (Loss) at September 30, 2021	9
Cash Flow Hedges of Existing Debt \| SOUTHERN POWER CO \| June 2022
Derivative [Line Items]
Pay Notional	$ 677
Pay Rate	2.95%
Receive Notional \| €		600
Receive Rate	1.00%
Fair Value Gain (Loss) at September 30, 2021	$ 9
Cash Flow Hedges of Existing Debt \| SOUTHERN POWER CO \| June 2026
Derivative [Line Items]
Pay Notional	$ 564
Pay Rate	3.78%
Receive Notional \| €		€ 500
Receive Rate	1.85%
Fair Value Gain (Loss) at September 30, 2021	$ 0

Derivatives - Schedule of Deriv

Derivatives - Schedule of Derivative Category and Balance Sheet Location (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	$ 546	$ 810
Derivative asset, Gross amounts offset	(57)	(529)
Derivative asset, net amounts recognized in the balance sheets	489	281
Derivative liability, gross amount recognized	103	621
Derivative liability, Gross amounts offset	(37)	(557)
Derivative liability, net amounts recognized in the balance sheets	66	64
Collateral already posted, assets, aggregate fair value	(20)
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	30	658
Derivative liability, gross amount recognized	29	563
Derivatives not designated as hedging instruments \| Energy-related derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	29	388
Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	29	331
Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	1	270
Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	232
Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	426	42
Derivative liability, gross amount recognized	15	30
Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	308	24
Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	9	11
Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	118	18
Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	6	19
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	90	110
Derivative liability, gross amount recognized	59	28
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	41	3
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	5
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	4	0
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	0
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	25	20
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	0
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	0	0
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	16	0
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	9	0
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	33	23
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	11	87
Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	10	0
ALABAMA POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	109	12
Derivative asset, Gross amounts offset	(3)	(7)
Derivative asset, net amounts recognized in the balance sheets	106	5
Derivative liability, gross amount recognized	4	7
Derivative liability, Gross amounts offset	(3)	(7)
Derivative liability, net amounts recognized in the balance sheets	1	0
ALABAMA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	104	12
Derivative liability, gross amount recognized	4	7
ALABAMA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	67	7
ALABAMA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	2	2
ALABAMA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	37	5
ALABAMA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	2	5
ALABAMA POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	5	0
ALABAMA POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	0
GEORGIA POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	166	15
Derivative asset, Gross amounts offset	(3)	(12)
Derivative asset, net amounts recognized in the balance sheets	163	3
Derivative liability, gross amount recognized	4	13
Derivative liability, Gross amounts offset	(3)	(12)
Derivative liability, net amounts recognized in the balance sheets	1	1
GEORGIA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	166	15
Derivative liability, gross amount recognized	4	13
GEORGIA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	124	7
GEORGIA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	2	5
GEORGIA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	42	8
GEORGIA POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	2	8
MISSISSIPPI POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	105	9
Derivative asset, Gross amounts offset	(2)	(7)
Derivative asset, net amounts recognized in the balance sheets	103	2
Derivative liability, gross amount recognized	3	9
Derivative liability, Gross amounts offset	(2)	(7)
Derivative liability, net amounts recognized in the balance sheets	1	2
MISSISSIPPI POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	105	9
Derivative liability, gross amount recognized	3	9
MISSISSIPPI POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	66	4
MISSISSIPPI POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	1	3
MISSISSIPPI POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	39	5
MISSISSIPPI POWER CO \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	2	6
SOUTHERN POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	30	89
Derivative asset, Gross amounts offset	(1)	0
Derivative asset, net amounts recognized in the balance sheets	29	89
Derivative liability, gross amount recognized	13	26
Derivative liability, Gross amounts offset	(1)	0
Derivative liability, net amounts recognized in the balance sheets	12	26
SOUTHERN POWER CO \| Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	1	0
Derivative liability, gross amount recognized	2	1
SOUTHERN POWER CO \| Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	1	0
SOUTHERN POWER CO \| Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	2	1
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	29	89
Derivative liability, gross amount recognized	11	25
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	8	2
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	2
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	1	0
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	0
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	9	0
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	11	23
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	11	87
SOUTHERN POWER CO \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Foreign currency derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	0
SOUTHERN Co GAS
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	122	665
Derivative asset, Gross amounts offset	(48)	(503)
Derivative asset, net amounts recognized in the balance sheets	74	162
Derivative liability, gross amount recognized	35	566
Derivative liability, Gross amounts offset	(28)	(531)
Derivative liability, net amounts recognized in the balance sheets	7	35
Collateral already posted, assets, aggregate fair value	(20)	28
SOUTHERN Co GAS \| Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	29	658
Derivative liability, gross amount recognized	27	562
SOUTHERN Co GAS \| Derivatives not designated as hedging instruments \| Energy-related derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	28	388
SOUTHERN Co GAS \| Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	27	330
SOUTHERN Co GAS \| Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	1	270
SOUTHERN Co GAS \| Derivatives not designated as hedging instruments \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	232
SOUTHERN Co GAS \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	51	6
Derivative liability, gross amount recognized	4	1
SOUTHERN Co GAS \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	51	6
SOUTHERN Co GAS \| Derivatives designated as hedging instruments for regulatory purposes \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	4	1
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	42	1
Derivative liability, gross amount recognized	4	3
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	33	1
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	3
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	3	0
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Energy-related derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	0
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	6	0
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	0	0
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	4	0
SOUTHERN Co GAS \| Derivatives designated as hedging instruments in cash flow and fair value hedges \| Derivatives designated as hedging instruments for regulatory purposes \| Interest rate derivatives \| Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	$ 0	$ 0

Derivatives - Schedule of Pre-t

Derivatives - Schedule of Pre-tax Effects of Unrealized Derivative Gains (Losses) (Details) - Energy-related derivatives - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	$ 404	$ 12
Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(5)
Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)		(2)
Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	297	12
Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	112	2
ALABAMA POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	100	6
ALABAMA POWER CO \| Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(1)
ALABAMA POWER CO \| Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)		0
ALABAMA POWER CO \| Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	66	5
ALABAMA POWER CO \| Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	35	1
GEORGIA POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	162	2
GEORGIA POWER CO \| Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(1)
GEORGIA POWER CO \| Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)		(1)
GEORGIA POWER CO \| Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	123	2
GEORGIA POWER CO \| Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	40	1
MISSISSIPPI POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	103	0
MISSISSIPPI POWER CO \| Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	0
MISSISSIPPI POWER CO \| Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)		(1)
MISSISSIPPI POWER CO \| Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	66	1
MISSISSIPPI POWER CO \| Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	37	0
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	39	4
SOUTHERN Co GAS \| Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(3)
SOUTHERN Co GAS \| Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)		0
SOUTHERN Co GAS \| Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	42	4
SOUTHERN Co GAS \| Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	$ 0	$ 0

Derivatives - Schedule of Pre_2

Derivatives - Schedule of Pre-Tax Effects of Hedging on AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ 3	$ 64	$ (17)	$ (35)
Cash Flow Hedging \| Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	38	9	59	2
Cash Flow Hedging \| Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	5	1	7	(27)
Cash Flow Hedging \| Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(36)	54	(79)	(10)
Fair Value Hedging \| Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(4)	0	(4)	0
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(28)	59	(63)	(8)
Southern Power \| Cash Flow Hedging \| Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	8	5	16	2
Southern Power \| Cash Flow Hedging \| Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(36)	54	(79)	(10)
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	30	5	43	(24)
SOUTHERN Co GAS \| Cash Flow Hedging \| Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	30	4	43	0
SOUTHERN Co GAS \| Cash Flow Hedging \| Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ 0	$ 1	$ 0	$ (24)

Derivatives - Schedule of Pre_3

Derivatives - Schedule of Pre-Tax Effects of Cash Flow and Fair Value Hedging on Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative [Line Items]
Depreciation and amortization	$ 896	$ 889	$ 2,658	$ 2,619
Total interest expense, net of amounts capitalized	(451)	(443)	(1,352)	(1,343)
Total other income (expense), net	131	113	297	319
Natural gas
Derivative [Line Items]
Total cost of sales	129	71	943	654
Other Income (Expense)
Derivative [Line Items]
Amount excluded from effectiveness testing recognized in earnings	4	0	4	0
Cash Flow Hedging \| Energy-related derivatives \| Cost of Sales
Derivative [Line Items]
Gain (loss) on hedges	2	0	0	(8)
Cash Flow Hedging \| Energy-related derivatives \| Depreciation and Amortization
Derivative [Line Items]
Gain (loss) on hedges	3	(1)	6	(3)
Cash Flow Hedging \| Interest rate derivatives \| Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(7)	(6)	(20)	(19)
Cash Flow Hedging \| Foreign currency derivatives \| Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(6)	(6)	(18)	(18)
Cash Flow Hedging \| Foreign currency derivatives \| Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	(34)	56	(76)	52
Fair Value Hedging \| Interest rate derivatives \| Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(4)	(3)	(16)	27
Fair Value Hedging \| Foreign currency derivatives \| Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	(32)	0	(32)	0
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	132	129	383	367
Total interest expense, net of amounts capitalized	(36)	(36)	(111)	(114)
Total other income (expense), net	2	13	10	19
SOUTHERN POWER CO \| Cash Flow Hedging \| Energy-related derivatives \| Depreciation and Amortization
Derivative [Line Items]
Gain (loss) on hedges	3	(1)	6	(3)
SOUTHERN POWER CO \| Cash Flow Hedging \| Foreign currency derivatives \| Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(6)	(6)	(18)	(18)
SOUTHERN POWER CO \| Cash Flow Hedging \| Foreign currency derivatives \| Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	$ (34)	$ 56	$ (76)	$ 52

Derivatives - Schedule of Cumul

Derivatives - Schedule of Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Securities due within one year
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ 0	$ (1,509)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	0	(10)
Long-term debt
Derivative [Line Items]
Carrying Amount of the Hedged Item	(3,320)	0
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	0	0
Long-term debt \| SOUTHERN Co GAS
Derivative [Line Items]
Carrying Amount of the Hedged Item	(497)	0
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ (1)	$ 0

Derivatives - Schedule of Pre_4

Derivatives - Schedule of Pre-tax Effect of Interest Rate and Energy Related Derivatives on Income (Details) - Derivatives not designated as hedging instruments - Energy-related derivatives - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 18	$ (25)	$ (86)	$ 72
Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(2)	(30)	(122)	54
Cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 20	$ 5	$ 36	$ 18

Acquisitions and Dispositions -

Acquisitions and Dispositions - Southern Company Narrative (Details) - Subsequent Event - USD ($) $ in Millions	Oct. 29, 2021	Dec. 31, 2021
Lessor, Lease, Description [Line Items]
Proceeds from sale of assets subject to leveraged lease	$ 45
Scenario, Forecast
Lessor, Lease, Description [Line Items]
Leveraged leases, income tax benefits		$ 16

Acquisitions and Dispositions_2

Acquisitions and Dispositions - Schedule of Asset Acquisition (Details) - SOUTHERN POWER CO - Deuel Harvest	9 Months Ended
	Sep. 30, 2021MW
Business Acquisition [Line Items]
Approximate nameplate capacity (in MWs)	300
Maximum
Business Acquisition [Line Items]
PPA Contract Period	25 years
Minimum
Business Acquisition [Line Items]
PPA Contract Period	15 years
Deuel Harvest
Business Acquisition [Line Items]
Ownership percentage by parent	100.00%

Acquisitions and Dispositions_3

Acquisitions and Dispositions - Southern Power Narrative (Details) $ in Millions	1 Months Ended	9 Months Ended
	Sep. 30, 2021USD ($)MW	Sep. 30, 2021USD ($)MW	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Business Acquisition [Line Items]
Construction work in progress	$ 9,611	$ 9,611		$ 8,697
Gain on sale		171	$ 36
SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress	$ 274	274		$ 127
Gain on sale		39	$ 39
SOUTHERN POWER CO \| Wind Generating Facility
Business Acquisition [Line Items]
Gain on sale		$ 37
SOUTHERN POWER CO \| Garland Solar Storage
Business Acquisition [Line Items]
Nameplate capacity placed in service (in MWs) \| MW	45	45
SOUTHERN POWER CO \| Series of Construction Projects
Business Acquisition [Line Items]
Construction costs incurred to date	$ 341	$ 341
Construction work in progress	228	228
SOUTHERN POWER CO \| Series of Construction Projects \| Minimum
Business Acquisition [Line Items]
Estimated future construction payments	400	400
SOUTHERN POWER CO \| Series of Construction Projects \| Maximum
Business Acquisition [Line Items]
Estimated future construction payments	$ 460	$ 460

Acquisitions and Dispositions_4

Acquisitions and Dispositions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2021	Mar. 31, 2022	Sep. 30, 2021	Dec. 31, 2020
Garland Solar Storage
Business Acquisition [Line Items]
Nameplate capacity placed in service (in MWs)	45				45
Garland Solar Storage \| Scenario, Forecast
Business Acquisition [Line Items]
Nameplate capacity placed in service (in MWs)		43
Garland Solar Storage \| Scenario, Forecast \| Subsequent Event
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		88	88
PPA Contract Period			20 years
Tranquillity Solar Storage \| Scenario, Forecast \| Subsequent Event
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				72
PPA Contract Period				20 years
Glass Sands \| Scenario, Forecast \| Subsequent Event
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		118	118
PPA Contract Period		12 years
Glass Sands \| Glass Sands
Business Acquisition [Line Items]
Ownership percentage by parent						100.00%

Acquisitions and Dispositions_5

Acquisitions and Dispositions - Southern Company Gas Narrative (Details) $ in Millions	Jul. 01, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Feb. 28, 2022USD ($)	Apr. 22, 2021USD ($)	Jun. 30, 2020payment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale				$ 171	$ 36
SOUTHERN Co GAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale				127	$ (2)
Deferred tax expense, increase from change in appointment rate			$ 85	85
SOUTHERN Co GAS \| Sequent \| Disposal Group, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale price	$ 159
Gain on sale	121
Gain on sale, net of tax	$ 93
Deferred tax expense, increase from change in appointment rate		$ 85
Guarantor obligations, current carrying value		36	36	36
Guarantor obligations		$ 1,000	$ 1,000	$ 1,000
SOUTHERN Co GAS \| Pivotal LNG \| Disposal Group, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of contingent milestone payments \| payment								2
Contingent milestone payment, amount							$ 5
SOUTHERN Co GAS \| Scenario, Forecast \| Pivotal LNG \| Disposal Group, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contingent milestone payment, amount						$ 5

Acquisitions and Dispositions_6

Acquisitions and Dispositions - Schedule of Assets Held for Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets Held for Sale:
Total property, plant, and equipment	$ 6	$ 8
Leveraged leases	45	52
Total Assets Held for Sale	$ 51	$ 60

Segment and Related Informati_3

Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)state	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)statesegment	Sep. 30, 2020USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	3		3
Operating revenues	$ 5,732	$ 5,755	$ 18,066	$ 15,771
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	501	332	1,113	851
SOUTHERN POWER CO \| Traditional Electric Operating Companies \| Wholesale revenues, affiliates
Segment Reporting Information [Line Items]
Operating revenues	$ 167	101	$ 361	279
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	4		4
Operating revenues	$ 605	950	$ 4,930	3,506
Number of reportable segments \| segment			4
SOUTHERN Co GAS \| SOUTHERN POWER CO \| Natural gas
Segment Reporting Information [Line Items]
Operating revenues		$ 9	$ 18	$ 22
Southern Natural Gas Company, LLC \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%		50.00%
PennEast Pipeline \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	20.00%		20.00%
Dalton Pipeline \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%		50.00%
Atlantic Coast Pipeline \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	5.00%		5.00%

Segment and Related Informati_4

Segment and Related Information - Schedule of Financial Data for Business Segments (Details) - USD ($) $ in Millions	Jul. 01, 2021	Sep. 30, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues			$ 6,238			$ 5,620	$ 17,346	$ 15,258
Segment net income (loss)			1,101			1,251	2,608	2,732
Goodwill		$ 5,280	5,280				5,280		$ 5,280
Assets held for sale		51	51				51		60
Total assets		127,861	127,861				127,861		122,935
Gain on sale							171	36
Estimated loss on Plant Vogtle Units 3 and 4			264			0	772	149
Impairment of leveraged leases			0			0	7	154
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues			679			523	1,610	1,337
Total assets		13,611	13,611				13,611		13,235
Gain on sale							39	39
SOUTHERN POWER CO \| Wind Generating Facility
Segment Reporting Information [Line Items]
Gain on sale							37
Gain on sale, net of tax							28
SOUTHERN POWER CO \| Disposal Group, Disposed of by Sale \| Plant Mankato
Segment Reporting Information [Line Items]
Gain on sale								39
Gain on sale, net of tax								23
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			623			477	2,994	2,362
Segment net income (loss)			56			14	389	360
Goodwill		5,015	5,015				5,015		5,015
Total assets		22,958	22,958				22,958		22,630
Gain on sale							127	(2)
Deferred tax expense, increase from change in appointment rate			85				85
Asset impairment charges							84	0
SOUTHERN Co GAS \| Disposal Group, Disposed of by Sale \| Sequent
Segment Reporting Information [Line Items]
Gain on sale	$ 121
Gain on sale, net of tax	$ 93
Deferred tax expense, increase from change in appointment rate		85
GEORGIA POWER CO
Segment Reporting Information [Line Items]
Operating revenues			2,856			2,617	7,050	6,371
Total assets		48,932	48,932				48,932		47,080
Estimated loss on Plant Vogtle Units 3 and 4			264	$ 460	$ 48	0	772	149
Estimated loss on Plant Vogtle Units 3 and 4, net of tax			197	$ 343	$ 36		576	111
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			5,527			5,049	14,051	12,628
Segment net income (loss)			1,163			1,358	2,563	2,783
Goodwill		2	2				2		2
Assets held for sale		3	3				3		5
Total assets		101,960	101,960				101,960		98,041
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			623			477	2,994	2,362
All Other
Segment Reporting Information [Line Items]
Impairment of leveraged leases							7	154
Impairment of leveraged lease, net of tax							6	74
Gas distribution operations \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill		4,034	4,034				4,034		4,034
Wholesale Gas Services \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			0			(51)	188	(19)
Gas marketing services \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill		981	981				981		981
Operating Segments \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			616			475	2,989	2,363
Segment net income (loss)			147			21	479	372
Total assets		23,763	23,763				23,763		23,040
Operating Segments \| Traditional Electric Operating Companies \| Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			5,018			4,629	12,813	11,576
Segment net income (loss)			1,085			1,284	2,352	2,571
Goodwill		0	0				0		0
Assets held for sale		3	3				3		5
Total assets		89,057	89,057				89,057		85,486
Operating Segments \| SOUTHERN POWER CO \| Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			679			523	1,610	1,337
Segment net income (loss)			78			74	211	212
Goodwill		2	2				2		2
Assets held for sale		0	0				0		0
Total assets		13,611	13,611				13,611		13,235
Operating Segments \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			623			477	2,994	2,362
Segment net income (loss)			56			14	389	360
Goodwill		5,015	5,015				5,015		5,015
Assets held for sale		0	0				0		0
Total assets		22,958	22,958				22,958		22,630
Operating Segments \| All Other
Segment Reporting Information [Line Items]
Operating revenues			124			132	412	380
Segment net income (loss)			(121)			(122)	(338)	(420)
Goodwill		263	263				263		263
Assets held for sale		48	48				48		55
Total assets		3,704	3,704				3,704		3,168
Operating Segments \| All Other \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			11			8	29	24
Segment net income (loss)			(91)			(7)	(90)	(12)
Total assets		11,387	11,387				11,387		11,336
Operating Segments \| Gas distribution operations \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			556			479	2,466	2,086
Segment net income (loss)			45			46	308	284
Total assets		20,619	20,619				20,619		19,090
Operating Segments \| Gas Pipeline Investments \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			8			8	24	24
Segment net income (loss)			10			23	3	74
Total assets		1,478	1,478				1,478		1,597
Operating Segments \| Wholesale Gas Services \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			0			(51)	188	(19)
Segment net income (loss)			94			(45)	108	(45)
Total assets		132	132				132		850
Operating Segments \| Gas marketing services \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			52			39	311	272
Segment net income (loss)			(2)			(3)	60	59
Total assets		1,534	1,534				1,534		1,503
Eliminations
Segment Reporting Information [Line Items]
Operating revenues			(36)			(38)	(111)	(112)
Segment net income (loss)			3			1	(6)	9
Goodwill		0	0				0		0
Assets held for sale		0	0				0		0
Total assets		(761)	(761)				(761)		(904)
Eliminations \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			(4)			(6)	(24)	(25)
Segment net income (loss)			0			0	0	0
Total assets		(12,192)	(12,192)				(12,192)		(11,746)
Eliminations \| Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			(170)			(103)	(372)	(285)
Segment net income (loss)			0			$ 0	0	$ 0
Goodwill		0	0				0		0
Assets held for sale		0	0				0		0
Total assets		$ (708)	$ (708)				$ (708)		$ (680)

Segment and Related Informati_5

Segment and Related Information - Schedule of Financial Data for Products and Services (Details) - USD ($) $ in Millions	Jul. 01, 2021	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Concentration Risk [Line Items]
Operating revenues			$ 6,238	$ 5,620	$ 17,346	$ 15,258
Gain on sale					171	36
Retail
Concentration Risk [Line Items]
Operating revenues			4,551	4,243	11,492	10,503
Wholesale
Concentration Risk [Line Items]
Operating revenues			731	584	1,822	1,473
Other
Concentration Risk [Line Items]
Operating revenues			179	164	525	484
Electric Utilities' Revenues
Concentration Risk [Line Items]
Operating revenues			5,527	5,049	14,051	12,628
Electric Utilities' Revenues \| Retail
Concentration Risk [Line Items]
Operating revenues			4,551	4,243	11,492	10,503
Electric Utilities' Revenues \| Wholesale
Concentration Risk [Line Items]
Operating revenues			731	584	1,822	1,473
Electric Utilities' Revenues \| Other
Concentration Risk [Line Items]
Operating revenues			245	222	737	652
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues			623	477	2,994	2,362
Southern Company Gas' Revenues \| Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues			553	476	2,451	2,072
Southern Company Gas' Revenues \| Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	(51)	188	(19)
Southern Company Gas' Revenues \| Gas marketing services
Concentration Risk [Line Items]
Operating revenues			52	39	311	272
Southern Company Gas' Revenues \| Other
Concentration Risk [Line Items]
Operating revenues			18	13	44	37
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues			623	477	2,994	2,362
Gain on sale					127	(2)
Deferred tax expense, increase from change in appointment rate			85		85
Asset impairment charges					84	0
Southern Company Gas' Revenues \| Disposal Group, Disposed of by Sale \| Sequent
Concentration Risk [Line Items]
Gain on sale	$ 121
Gain on sale, net of tax	$ 93
Deferred tax expense, increase from change in appointment rate		$ 85
Southern Company Gas' Revenues \| Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	(51)	188	(19)
Less Gross Gas Costs			0	1,134	3,783	3,189
Third Party Gross Revenues \| Southern Company Gas' Revenues \| Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	1,050	3,881	3,089
Intercompany Revenues \| Southern Company Gas' Revenues \| Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			0	33	90	81
Total Gross Revenues \| Southern Company Gas' Revenues \| Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues			$ 0	$ 1,083	$ 3,971	$ 3,170