NiSource (NI) 10-Q8 May 242024 Q1 Quarterly reportFinancial data

Company Profile

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
Document And Entity Information - shares	Mar. 31, 2024	Apr. 30, 2024
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-16189
Entity Registrant Name	NiSource Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	35-2108964
Entity Address, Address Line One	801 East 86th Avenue
Entity Address, City or Town	Merrillville,
Entity Address, State or Province	IN
Entity Address, Postal Zip Code	46410
City Area Code	(877)
Local Phone Number	647-5990
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		448,305,338
Entity Central Index Key	0001111711
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	NI
Security Exchange Name	NYSE

Statements Of Consolidated Inco

Statements Of Consolidated Income (Loss) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Revenues
Customer revenues	$ 1,643	$ 1,896.1
Other revenues	63.3	69.9
Total Operating Revenues	1,706.3	1,966
Operating Expenses
Cost of energy	425	765.1
Operation and maintenance	378.4	391.2
Depreciation and amortization	242.1	206.9
Other taxes	77.4	71.8
Operating Costs and Expenses	1,122.9	1,435
Operating Income	583.4	531
Other Income (Deductions)
Interest expense, net	(116.3)	(108.9)
Other, net	9.2	1.5
Total Other Deductions, Net	(107.1)	(107.4)
Income before Income Taxes	476.3	423.6
Income Taxes	76	85.8
Net Income	400.3	337.8
Net income (loss) attributable to noncontrolling interest	35.3	4.8
Net Income Attributable to NiSource	365	333
Preferred Stock Redemption Premium	(14)	0
Preferred dividends	(6.7)	(13.8)
Net Income Available to Common Shareholders	$ 344.3	$ 319.2
Earnings Per Share
Basic Earnings Per Share	$ 0.77	$ 0.77
Diluted Earnings Per Share	$ 0.77	$ 0.71
Basic Average Common Shares Outstanding	447.9	412.8
Diluted Average Common Shares	449.4	447.1
Noncontrolling Interest
Other Income (Deductions)
Net income (loss) attributable to noncontrolling interest		$ 4.8
Preferred Stock Redemption Premium	$ 0

Statements of Consolidated Comp

Statements of Consolidated Comprehensive Income (Loss) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Net Income		$ 400.3	$ 337.8
Other comprehensive income:
Net unrealized loss on available-for-sale securities	[1]	(0.3)	2
Net unrealized gain (loss) on cash flow hedges	[2]	(0.1)	0.1
Unrecognized pension and OPEB benefit (costs)	[3]	0.2	0.3
Total other comprehensive income (loss)		(0.2)	2.4
Comprehensive Income		$ 400.1	$ 340.2

[1] Net unrealized loss on available-for-sale debt securities, net of $0.1 million tax benefit and $0.5 million tax expense in the first quarter of 2024 and 2023, respectively. Unrecognized pension and OPEB benefit (costs), net of $0.1 million of tax expense and $0.1 million tax expense in the first quarter of 2024 and 2023, respectively.

Statements of Consolidated Co_2

Statements of Consolidated Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	$ 0.1	$ (0.5)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, Tax	0	0.1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	$ (0.1)	$ (0.1)

Statements of Consolidated Bala

Statements of Consolidated Balance Sheets - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment
Plant		$ 31,300.6	$ 30,482.1
Accumulated depreciation and amortization		(8,354.5)	(8,207.2)
Net Property, Plant and Equipment	[1]	22,946.1	22,274.9
Investments and Other Assets
Unconsolidated affiliates		5.4	5.3
Available-for-sale debt securities (amortized cost of $160.2 and $169.0, allowance for credit losses of $0.4 and $0.6, respectively)		150.1	159.1
Other investments		86.8	82.7
Total Investments and Other Assets		242.3	247.1
Current Assets
Cash and cash equivalents		102.2	2,245.4
Restricted Cash		38.3	35.7
Accounts receivable		877.2	884.9
Allowance for credit losses		(31.6)	(22.9)
Accounts receivable, net		845.6	862
Gas storage		70.1	265.8
Materials and supplies, at average cost		187.2	172.1
Electric production fuel, at average cost		66.3	65.3
Exchange gas receivable		43.2	66
Regulatory assets		260.4	214.3
Prepayments and other		161.1	118.6
Total Current Assets	[1]	2,060.2	4,499.4
Other Assets
Regulatory assets		2,231.7	2,245.9
Goodwill		1,485.9	1,485.9
Deferred charges and other		371.9	324
Total Other Assets		4,089.5	4,055.8
Total Assets		29,338.1	31,077.2
Stockholders' Equity
Common stock - $0.01 par value,750,000,000 shares authorized; 448,197,604 and 447,381,671 shares outstanding, respectively		$ 4.5	$ 4.5
Preferred Stock, Shares Outstanding		0	40,000
Preferred stock - $0.01 par value, 20,000,000 shares authorized; 0 and 40,000 shares outstanding, respectively		$ 0	$ 486.1
Treasury stock		(99.9)	(99.9)
Additional paid-in capital		8,886.8	8,879.5
Retained deficit		(861.7)	(967)
Accumulated other comprehensive loss		(33.8)	(33.6)
Total NiSource Stockholders’ Equity		7,895.9	8,269.6
Noncontrolling interest in consolidated subsidiaries		1,899	1,866.7
Total Stockholders' Equity		9,794.9	10,136.3
Long-term debt, excluding amounts due within one year		11,724.6	11,055.5
Total Capitalization		21,519.5	21,191.8
Current Liabilities
Current portion of long-term debt		24	23.8
Short-term borrowings		1,222.3	3,048.6
Accounts payable		612.5	749.4
Dividends payable - common stock		119	0
Customer deposits and credits		189.5	294.4
Taxes accrued		169.5	166.2
Interest accrued		148.6	136.1
Exchange gas payable		17.1	50.5
Regulatory liabilities		237.6	278.6
Asset Retirement Obligation		78	72.5
Accrued compensation and employee benefits		136	227.6
Other accruals		170.9	217.4
Total Current Liabilities	[2]	3,125	5,265.1
Other Liabilities
Deferred income taxes		2,159.5	2,080.4
Accrued liability for postretirement and postemployment benefits		244.8	250.1
Regulatory liabilities		1,482	1,510.7
Asset retirement obligations		509.6	480.5
Other noncurrent liabilities		297.7	298.6
Total Other Liabilities	[2]	4,693.6	4,620.3
Total Capitalization and Liabilities		$ 29,338.1	$ 31,077.2
Common Stock, Shares Authorized		750,000,000	750,000,000
Common Stock, No Par Value		$ 0.01	$ 0.01
Deposits to renewable generation asset developer		$ 285.8	$ 454.2
Joint Ventures
Property, Plant and Equipment
Net Property, Plant and Equipment		1,358.2
Current Assets
Total Current Assets		60.8	63.6
Current Liabilities
Total Current Liabilities		60.9	68.3
Other Liabilities
Total Other Liabilities		$ 56.3	$ 55.7

[1] Includes $1,358.2 million and $1,369.8 million at March 31, 2024 and December 31, 2023, respectively, of net property, plant and equipment assets and $60.8 million and $63.6 million at March 31, 2024 and December 31, 2023, respectively, of current assets of consolidated VIEs that may be used only to settle obligations of the consolidated VIEs. Note 4, "Noncontrolling Interests," for additional information. Includes $60.9 million and $68.3 million at March 31, 2024 and December 31, 2023, respectively, of current liabilities and $56.3 million and $55.7 million at March 31, 2024 and December 31, 2023, respectively, of other liabilities of consolidated VIEs that creditors do not have recourse to our general credit. Refer to Note 4, "Noncontrolling Interests," for additional information.

Statements of Consolidated Ba_2

Statements of Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Amortized Cost		$ 160.2	$ 169
Allowance for Credit Loss		$ 0.4	$ 0.6
Common Stock, Shares Authorized		750,000,000	750,000,000
Common Stock, Shares, Outstanding		448,197,604	447,381,671
Preferred Stock, Par or Stated Value Per Share		$ 0.01	$ 0.01
Preferred Stock, Shares Authorized		20,000,000	20,000,000
Preferred Stock, Shares Outstanding		0	40,000
Public Utilities, Property, Plant and Equipment, Net	[1]	$ 22,946.1	$ 22,274.9
Current assets	[1]	2,060.2	4,499.4
Current liabilities	[2]	3,125	5,265.1
Other Liabilities	[2]	4,693.6	4,620.3
Deposits to renewable generation asset developer		285.8	454.2
Joint Ventures
Public Utilities, Property, Plant and Equipment, Net		1,358.2
Current assets		60.8	63.6
Current liabilities		60.9	68.3
Other Liabilities		$ 56.3	$ 55.7

[1] Includes $1,358.2 million and $1,369.8 million at March 31, 2024 and December 31, 2023, respectively, of net property, plant and equipment assets and $60.8 million and $63.6 million at March 31, 2024 and December 31, 2023, respectively, of current assets of consolidated VIEs that may be used only to settle obligations of the consolidated VIEs. Note 4, "Noncontrolling Interests," for additional information. Includes $60.9 million and $68.3 million at March 31, 2024 and December 31, 2023, respectively, of current liabilities and $56.3 million and $55.7 million at March 31, 2024 and December 31, 2023, respectively, of other liabilities of consolidated VIEs that creditors do not have recourse to our general credit. Refer to Note 4, "Noncontrolling Interests," for additional information.

Statements Of Consolidated Cash

Statements Of Consolidated Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Activities
Net Income	$ 400.3	$ 337.8
Adjustments to Reconcile Net Income to Net Cash from Operating Activities:
Depreciation and amortization	242.1	206.9
Deferred income taxes and investment tax credits	61.6	75.5
Asset Retirement Obligation, Cash Paid to Settle	(12)	(5.5)
Other adjustments	7.8	1.1
Changes in Assets and Liabilities:
Components of working capital	(235.2)	71.1
Regulatory assets/liabilities	18.4	11
Deferred charges and other noncurrent assets	(18)	(12)
Other noncurrent liabilities and deferred credits	(8.8)	(2.5)
Net Cash Flows from Operating Activities	456.2	683.4
Investing Activities
Capital expenditures	(589.5)	(557.1)
Payment to renewable generation asset developer	(110.6)	(137.3)
Other investing activities	(22.9)	(33.4)
Net Cash Flows used for Investing Activities	(723)	(727.8)
Financing Activities
Proceeds from issuance of long-term debt	644.4	744.2
Repayments of finance lease obligations	(7.2)	(8.1)
Change in short-term borrowings, net (maturity ≤ 90 days)	(176.3)	(480.4)
Issuance of common stock, net of issuance costs	2.7	3
Equity costs, premiums and other debt related costs	(57.6)	(11.8)
Contributions from noncontrolling interests	0	3.6
Payments to Noncontrolling Interests	(3)	(5.3)
Dividends paid - common stock	(118.6)	(103.2)
Dividends paid - preferred stock	(8.1)	(8.1)
Contract liability payment	0	(16.6)
Net Cash Flows from Financing Activities	(1,873.8)	117.3
Change in cash, cash equivalents and restricted cash	(2,140.6)	72.9
Cash, cash equivalents and restricted cash at beginning of period	2,281.1	75.4
Cash, Cash Equivalents and Restricted Cash at End of Period	140.5	148.3
Preferred Stock Redemption Premium	(486.1)	0
Redemption Premium	(14)	0
Repayment of short-term debt (maturity greater than 90 days)	$ (1,650)	$ 0

Statement of Consolidated Cash

Statement of Consolidated Cash Flows (Schedule of Balance Sheet Reconciliation) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Cash and Cash Equivalents, at Carrying Value	$ 102.2	$ 2,245.4
Restricted Cash	38.3	35.7
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 140.5	$ 2,281.1	$ 148.3	$ 75.4

Statements Of Consolidated Ca_2

Statements Of Consolidated Cash Flows (Supplemental Disclosures of Cash Flow Information) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital expenditures included in current liabilities	$ 239.7	$ 261.1
Dividends declared but not paid	$ 119	$ 122.8

Statements Of Consolidated Equi

Statements Of Consolidated Equity - USD ($) $ in Millions	Total	Common Stock	Preferred Stock	Treasury Stock, Common	Additional Paid-in Capital	Retained Deficit	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest	Treasury Stock, Preferred
Beginning balance at Dec. 31, 2022	$ 7,901.8	$ 4.2	$ 1,546.5	$ (99.9)	$ 7,375.3	$ (1,213.6)	$ (37.1)	$ 326.4
Comprehensive Income:
Net Income	337.8	0	0	0	0	333	0
Other comprehensive income (loss), net of tax	2.4	0	0	0	0	0	2.4	0
Dividends:
Common stock	(206.7)	0	0	0	0	(206.7)	0	0
Preferred stock	(27.5)	0	0	0	0	(27.5)	0	0
Contributions from noncontrolling interest(2)	(3.6)	0	0		0	0	0	(3.6)	$ 0
Distributions to noncontrolling interests	5.3	0	0	0	0	0	0	(5.3)
Stock Issuances:
Employee stock purchase plan	1.3	0	0	0	1.3	0	0	0
Long-term incentive plan	(6.3)	0	0	0	(6.3)	0	0	0
401(k) and profit sharing	2.6	0	0	0	2.6	0	0	0
Ending balance at Mar. 31, 2023	8,003.7	4.2	1,546.5	(99.9)	7,372.9	(1,114.8)	(34.7)	329.5
Beginning balance at Dec. 31, 2023	10,136.3	4.5	486.1	(99.9)	8,879.5	(967)	(33.6)	1,866.7
Comprehensive Income:
Net Income	400.3	0	0	0	0	365	0
Other comprehensive income (loss), net of tax	(0.2)	0	0	0	0	0	(0.2)	0
Dividends:
Common stock	(237.6)	0	0	0	0	(237.6)	0	0
Preferred stock	(8.1)	0	0	0	0	(8.1)	0	0
Distributions to noncontrolling interests	3	0	0	0	0	0	0	(3)
Stock Issuances:
Equity Units	(486.1)	0	(486.1)		0	0	0	0	$ 0
Employee stock purchase plan	1.4	0	0	0	1.4	0	0	0
Long-term incentive plan	(3.3)	0	0	0	(3.3)	0	0	0
401(k) and profit sharing	2.6	0	0	0	2.6	0	0	0
Ending balance at Mar. 31, 2024	$ 9,794.9	$ 4.5	$ 0	$ (99.9)	$ 8,886.8	$ (861.7)	$ (33.8)	$ 1,899

Statements of Consolidated Eq_2

Statements of Consolidated Equity (Shares) - shares shares in Thousands	Total	Preferred Stock	Common Stock	Treasury Stock, Common
Beginning balance at Dec. 31, 2022	412,143	1,303	416,106	3,963
Issued (Redeemed):
Employee stock purchase plan	48	0	48	0
Long-term incentive plan	695	0	695	0
401(k) and profit sharing	97	0	97	0
Ending balance at Mar. 31, 2023	412,983	1,303	416,946	3,963
Beginning balance at Dec. 31, 2023	447,382	40	451,345	3,963
Issued (Redeemed):
Employee stock purchase plan	53	0	53	0
Long-term incentive plan	663	0	663	0
401(k) and profit sharing	100	0	100	0
Preferred Stock Shares Redeemed	0	(40)	0	0
Ending balance at Mar. 31, 2024	448,198	0	452,161	3,963

Statements Of Consolidated Eq_3

Statements Of Consolidated Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Common Stock, Dividends, Per Share, Declared	$ 0.53	$ 0.50
Preferred Stock Redemption Premium	$ (14)	$ 0
Distributions to noncontrolling interests		3.6
Preferred stock	(8.1)	(27.5)
Distributions to noncontrolling interests	(3)	(5.3)
Equity Units	(486.1)
Noncontrolling Interest
Preferred Stock Redemption Premium	0
Distributions to noncontrolling interests		3.6
Preferred stock	0	0
Distributions to noncontrolling interests	3	5.3
Equity Units	0
Common Stock
Preferred Stock Redemption Premium	0
Distributions to noncontrolling interests		0
Preferred stock	0	0
Distributions to noncontrolling interests	0	0
Equity Units	0
Preferred Stock
Preferred Stock Redemption Premium	0
Distributions to noncontrolling interests		0
Preferred stock	0	0
Distributions to noncontrolling interests	0	0
Equity Units	(486.1)
Treasury Stock, Common
Preferred Stock Redemption Premium	0
Preferred stock	0	0
Distributions to noncontrolling interests	0	0
Additional Paid-in Capital
Preferred Stock Redemption Premium	0
Distributions to noncontrolling interests		0
Preferred stock	0	0
Distributions to noncontrolling interests	0	0
Equity Units	0
Retained Deficit
Preferred Stock Redemption Premium	(14)
Distributions to noncontrolling interests		0
Preferred stock	(8.1)	(27.5)
Distributions to noncontrolling interests	0	0
Equity Units	0
Accumulated Other Comprehensive Income (Loss)
Preferred Stock Redemption Premium	0
Distributions to noncontrolling interests		0
Preferred stock	0	0
Distributions to noncontrolling interests	0	$ 0
Equity Units	0
Series B Preferred Stock
Preferred Stock Redemption Premium	$ (14)

Basis of Accounting Presentatio

Basis of Accounting Presentation	3 Months Ended
Basis of Accounting Presentation	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting Presentation	Our accompanying Condensed Consolidated Financial Statements (unaudited) reflect all normal recurring adjustments that are necessary, in the opinion of management, to present fairly the results of operations in accordance with GAAP in the United States of America. The accompanying financial statements include the accounts of us, our majority-owned subsidiaries, and VIEs of which we are the primary beneficiary after the elimination of all intercompany accounts and transactions. The accompanying financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2023. Income for interim periods may not be indicative of results for the calendar year due to weather variations and other factors. The Condensed Consolidated Financial Statements (unaudited) have been prepared pursuant to the rules and regulations of the SEC. Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations, although we believe that the disclosures made in this Quarterly Report on Form 10-Q are adequate to make the information herein not misleading.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
Recent Accounting Pronouncements	Mar. 31, 2024
Accounting Standards Update and Change in Accounting Principle [Abstract]
Recent Accounting Pronouncements

Revenue Recognition

Revenue Recognition	3 Months Ended
Revenue Recognition	Mar. 31, 2024
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer	Revenue Disaggregation and Reconciliation. We disaggregate revenue from contracts with customers based upon reportable segment, as well as by customer class. As of January 1, 2024, we have changed our reportable segments from Gas Distributions Operations and Electric Operations to Columbia Operations and NIPSCO Operations. Our historical segment disclosures have been recast to be consistent with the current presentation. For additional information see Note 17, "Business Segment Information." The Columbia Operations segment provides regulated natural gas service and transportation for residential, commercial and industrial customers in Ohio, Pennsylvania, Virginia, Kentucky, and Maryland. The NIPSCO Operations segment provides regulated gas and electric service in the northern part of Indiana. The tables below reconcile revenue disaggregation by customer class to segment revenue, as well as to revenues reflected on the Condensed Statements of Consolidated Income (unaudited): Three months ended March 31, 2024 (in millions) Columbia Operations NIPSCO Operations Corporate and Other Total Gas Distribution Residential $ 628.0 $ 212.1 $ — $ 840.1 Commercial 220.4 74.7 — 295.1 Industrial 40.1 23.8 — 63.9 Off-system 12.8 — — 12.8 Wholesale 0.8 — — 0.8 Miscellaneous (1) 8.2 7.9 — 16.1 Subtotal $ 910.3 $ 318.5 $ — $ 1,228.8 Electric Generation and Power Delivery Residential $ — $ 143.8 $ — $ 143.8 Commercial — 142.9 — 142.9 Industrial — 115.9 — 115.9 Wholesale — 6.3 — 6.3 Public Authority — 2.1 — 2.1 Miscellaneous (1) — 3.2 — 3.2 Subtotal $ — $ 414.2 $ — $ 414.2 Total Customer Revenues (2) 910.3 732.7 — 1,643.0 Other Revenues (3) 43.4 19.7 0.2 63.3 Total Operating Revenues $ 953.7 $ 752.4 $ 0.2 $ 1,706.3 (1) Amounts included in Columbia Operations are primarily related to earnings share mechanisms and late fees. Amounts included in NIPSCO Operations are primarily related to revenue refunds, public repairs and property rentals. (2) Customer revenue amounts exclude intersegment revenues. See Note 17, "Business Segment Information," for discussion of intersegment revenues. (3) Amounts included in Columbia Operations primarily relate to weather normalization adjustment mechanisms. Amounts included in NIPSCO Operations primarily relate to MISO multi-value projects and revenue from non-jurisdictional transmission assets. Three months ended March 31, 2023 (in millions) Columbia Operations NIPSCO Operations Corporate and Other Total Gas Distribution Residential $ 684.6 $ 302.4 $ — $ 987.0 Commercial 248.0 112.6 — 360.6 Industrial 40.4 31.5 — 71.9 Off-system 17.2 — — 17.2 Wholesale 1.0 — — 1.0 Miscellaneous (1) 11.8 5.6 — 17.4 Subtotal $ 1,003.0 $ 452.1 $ — $ 1,455.1 Electric Generation and Power Delivery Residential $ — $ 150.4 $ — $ 150.4 Commercial — 150.9 — 150.9 Industrial — 134.2 — 134.2 Wholesale — 2.6 — 2.6 Public Authority — 2.1 — 2.1 Miscellaneous (1) — 0.8 — 0.8 Subtotal $ — $ 441.0 $ — $ 441.0 Total Customer Revenues (2) 1,003.0 893.1 — 1,896.1 Other Revenues (3) 45.9 23.8 0.2 69.9 Total Operating Revenues $ 1,048.9 $ 916.9 $ 0.2 $ 1,966.0 (1) Amounts included in Columbia Operations are primarily related to earnings share mechanisms and late fees. Amounts included in NIPSCO Operations, are primarily related to revenue refunds, public repairs and property rentals. (2) Customer revenue amounts exclude intersegment revenues. See Note 17, "Business Segment Information," for discussion of intersegment revenues. (3) Amounts included in Columbia Operations are primarily relate to weather normalization adjustment mechanisms. Amounts included in NIPSCO Operations primarily relate to MISO multi-value projects and revenue from non-jurisdictional transmission assets. Customer Accounts Receivable. Accounts receivable on our Condensed Consolidated Balance Sheets (unaudited) includes both billed and unbilled amounts, as well as certain amounts that are not related to customer revenues. Unbilled amounts of accounts receivable relate to a portion of a customer’s consumption of gas or electricity from the date of the last cycle billing through the last day of the month (balance sheet date). Factors taken into consideration when estimating unbilled revenue include historical usage, customer rates, and weather. A significant portion of our operations are subject to seasonal fluctuations in sales. During the heating season, primarily from November through March, revenues and receivables from gas sales are more significant than in other months. The opening and closing balances of customer receivables for the three months ended March 31, 2024 are presented in the table below. We had no significant contract assets or liabilities during the period. Additionally, we have not incurred any significant costs to obtain or fulfill contracts. (in millions) Customer Accounts Receivable, Billed (less reserve) Customer Accounts Receivable, Unbilled (less reserve) Balance as of December 31, 2023 $ 479.4 $ 337.6 Balance as of March 31, 2024 552.1 263.6 Utility revenues are billed to customers monthly on a cycle basis. We expect that substantially all customer accounts receivable will be collected following customer billing, as this revenue consists primarily of periodic, tariff-based billings for service and usage. We maintain common utility credit risk mitigation practices, including requiring deposits and actively pursuing collection of past due amounts. Our regulated operations also utilize certain regulatory mechanisms that facilitate recovery of bad debt costs within tariff-based rates, which provides further evidence of collectibility. It is probable that substantially all of the consideration to which we are entitled from customers will be collected upon satisfaction of performance obligations. Allowance for Credit Losses. To evaluate for expected credit losses, customer account receivables are pooled based on similar risk characteristics, such as customer type, geography, payment terms, and related macro-economic risks. Expected credit losses are established using a model that considers historical collections experience, current information, and reasonable and supportable forecasts. Internal and external inputs are used in our credit model including, but not limited to, energy consumption trends, revenue projections, actual charge-offs data, recoveries data, shut-offs, customer delinquencies, final bill data, and inflation. We continuously evaluate available information relevant to assessing collectability of current and future receivables. We evaluate creditworthiness of specific customers periodically or following changes in facts and circumstances. When we become aware of a specific commercial or industrial customer's inability to pay, an allowance for expected credit losses is recorded for the relevant amount. We also monitor other circumstances that could affect our overall expected credit losses including, but not limited to, creditworthiness of overall population in service territories, adverse conditions impacting an industry sector, and current economic conditions. At each reporting period, we record expected credit losses to an allowance for credit losses account. When deemed to be uncollectible, customer accounts are written-off. A rollforward of our allowance for credit losses as of March 31, 2024 and December 31, 2023 are presented in the table below: ( in millions ) Columbia Operations NIPSCO Operations Corporate and Other Total Balance as of January 1, 2024 $ 10.2 $ 11.9 $ 0.8 $ 22.9 Current period provisions 11.0 3.6 — 14.6 Write-offs charged against allowance (7.3) (2.1) (0.8) (10.2) Recoveries of amounts previously written off 4.1 0.2 — 4.3 Balance as of March 31, 2024 $ 18.0 $ 13.6 $ — $ 31.6 ( in millions ) Columbia Operations NIPSCO Operations Corporate and Other Total Balance as of January 1, 2023 $ 11.1 $ 12.0 $ 0.8 $ 23.9 Current period provisions 28.3 11.5 — 39.8 Write-offs charged against allowance (49.2) (12.4) — (61.6) Recoveries of amounts previously written off 20.0 0.8 — 20.8 Balance as of December 31, 2023 $ 10.2 $ 11.9 $ 0.8 $ 22.9

Earnings Per Share

Earnings Per Share	3 Months Ended
Earnings Per Share	Mar. 31, 2024
Earnings Per Share [Abstract]
Earnings Per Share	The calculations of basic and diluted EPS are based on the weighted average number of shares of common stock and potential common stock outstanding during the period. For the three months ended March 31, 2024, the weighted-average shares outstanding for diluted EPS includes the incremental effects of the various long-term incentive compensation plans and an ATM forward agreement under the Treasury Stock Method when the impact would be dilutive (See Note 6, "Equity,"). For the purposes of determining diluted EPS, for the three months ended March 31, 2023, the shares underlying the purchase contracts included within the Equity Units were included in the calculation of potential common stock outstanding using the if-converted method under US GAAP and we assumed share settlement of the remaining purchase contract payment balance from our Equity Units based on the average share price during the period. A numerator adjustment was reflected in the calculation of diluted EPS for interest expense incurred in the three months ended March 31, 2023, net of tax, related to the purchase contracts. The purchase contracts were settled on December 1, 2023. We began using the two-class method of computing earnings per share in 2023 because we have participating securities in the form of non-vested restricted stock units with a non-forfeitable right to dividend equivalents, for which vesting is predicated solely on the passage of time. The calculation of earnings per share using the two-class method excludes income attributable to these participating securities from the numerator and excludes the dilutive impact of those shares from the denominator. The following table presents the calculation of our basic and diluted EPS: Three Months Ended (in millions, except per share amounts) 2024 2023 Numerator: Net Income Available to Common Shareholders $ 344.3 $ 319.2 Less: Income allocated to participating securities 0.3 0.2 Net Income Available to Common Shareholders - Basic 344.0 319.0 Add: Dilutive effect of Equity Units — 0.4 Net Income Available to Common Shareholders - Diluted $ 344.0 $ 319.4 Denominator: Average common shares outstanding - Basic 447.9 412.8 Dilutive potential common shares: Equity Units purchase contracts — 31.2 Equity Units purchase contract payment balance — 1.8 Shares contingently issuable under employee stock plans 0.9 0.8 Shares restricted under employee stock plans 0.4 0.5 ATM forward agreement 0.2 — Average Common Shares - Diluted 449.4 447.1 Earnings per common share: Basic 0.77 0.77 Diluted 0.77 0.71

Equity

Equity	3 Months Ended
Equity	Mar. 31, 2024
Equity [Abstract]
Equity	ATM Program. On February 22, 2024, we entered into eight separate equity distribution agreements pursuant to which we are able to sell up to an aggregate of $900.0 million of our common stock. On February 23, 2024, under the ATM program, we executed a forward sale agreement, which allows us to issue a fixed number of shares at a price to be settled in the future. On February 23, 2024, the forward purchaser under our forward sale agreement borrowed 7,757,951 shares from third parties, which the forward purchaser sold, through its affiliated agent, at a weighted average price of $25.78 per share. We may settle the forward sale agreement in shares, cash or net shares by December 20, 2024. Had we settled all the shares under the forward sale agreement at March 31, 2024, we would have received approximately $199.8 million, based on a net price of $25.76 per share. As of March 31, 2024, the ATM program (inclusive of the forward sale agreement) had approximately $700.0 million of equity available for issuance. The program expires on December 31, 2025. Preferred Stock . Dividends declared per share for the Series A Preferred Stock were zero and $28.25 during the three months ended March 31, 2024 and 2023, respectively. Dividends declared per share for the Series B Preferred Stock were $406.25 and $812.50 during the three months ended March 31, 2024 and 2023, respectively. On June 15, 2023, we redeemed all 400,000 outstanding shares of Series A Preferred Stock for a redemption price of $1,000 per share or $400.0 million in total. Series B and B-1 Preferred Stock. On March 15, 2024, we redeemed all 20,000 outstanding shares of Series B Preferred Stock for a redemption price of $25,000 per share and all 20,000 outstanding shares of Series B-1 Preferred Stock for a redemption price of $0.01 per share or $500.0 million in total. Following the redemption, dividends ceased to accrue on the shares of Series B Preferred Stock, shares of the Series B Preferred Stock and Series B-1 Preferred Stock were no longer deemed outstanding and all rights of the holders of such shares of Series B Preferred Stock and Series B-1 Preferred Stock terminated. In conjunction with the redemption, we recorded a $14.0 million preferred stock redemption premium, calculated as the difference between the carrying value on the redemption date of the Series B Preferred Stock and Series B-1 Preferred Stock and the total amount of consideration paid to redeem, which was recorded as a reduction to retained earnings during the first quarter of 2024. We did not recognize an excise tax liability under the IRA in connection with this redemption as we expect to issue common stock under the ATM program in 2024 in excess of the fair value of the Series B Preferred Stock and Series B-1 Preferred Stock redeemed. In March 2024, we filed a Certificate of Elimination to our Amended and Restated Certificate of Incorporation with the Secretary of State of Delaware to eliminate from the Amended and Restated Certificate of Incorporation all matters set forth in the Certificate of Designations with respect to the Series B Preferred Stock and the Certificate of Designations with respect to the Series B-1 Preferred Stock. As a result, the 20,000 shares that were previously designated as Series B Preferred Stock and the 20,000 shares that were previously designated as Series B-1 Preferred Stock were returned to the status of authorized but unissued shares of preferred stock, par value $0.01 per share, without designation as to series. The Certificate of Elimination does not change the total number of authorized shares of capital stock of NiSource or the total number of authorized shares of preferred stock. We voluntarily delisted the preferred stock from the New York Stock Exchange. Equity Units. On December 1, 2023, we issued 33,898,837 shares of our common stock under the purchase contract component of the Corporate Units. As of December 1, 2023, each holder of Corporate Units was deemed to have automatically delivered to us the related Series C Mandatory Convertible Preferred Stock that were components of the Corporate Units in full satisfaction of such holder’s obligations under the related purchase contract, and all shares of Series C Mandatory Convertible Preferred Stock were returned to the status of authorized but unissued preferred stock, par value of $0.01 per share, without designation as to series. We voluntarily delisted the Corporate Units from the New York Stock Exchange.

Gas in Storage

Gas in Storage	3 Months Ended
Gas in Storage	Mar. 31, 2024
Gas in Storage [Abstract]
Gas in Storage	We use both the LIFO inventory methodology and the weighted-average cost methodology to value natural gas in storage. Natural gas storage injections are priced at the average of the costs of natural gas supply purchased during the year. For interim periods, the difference in the cost of replacing the current portion of stored gas inventory compared to the amount stated on a LIFO basis is recorded within the Condensed Consolidated Balance Sheets (unaudited). Due to seasonality requirements, we expect interim variances in LIFO layers to be replenished by year end. The LIFO basis exceeded the cost of replacing the current portion of stored gas by $27.5 million and zero respectively, for the periods ended March 31, 2024 and December 31, 2023, for certain gas distribution companies recorded within "Prepayments and other" on the Condensed Consolidated Balance Sheets (unaudited).

Regulatory Matters

Regulatory Matters	3 Months Ended
Regulatory Matters	Mar. 31, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Renewable generation filings In March 2024, NIPSCO filed a petition with the IURC to, after notice and hearing, issue an order modifying its November 22, 2023 order to approve direct ownership of the Gibson Project. The hearing is scheduled for June 2024 with a final order expected August 2024. In March 2024, NIPSCO also filed a petition with the IURC to, after notice and hearing, issue an order modifying its June 29, 2021 order to approve direct ownership of the Fairbanks Project. The hearing is scheduled for July 2024 with a final order expected September of 2024. WAM system filing In March 2024, NIPSCO filed a petition with the IURC for authority to defer, as a regulatory asset, certain costs, including depreciation and amortization incurred in connection with improvements to its information technology systems through the design, development, and implementation of a new WAM program for the scheduling, dispatch, and execution of work and the management of underlying assets. These improvements are part of our enterprise-wide transformation roadmap which seeks to optimize our field work. The petition also included the confirmation that the WAM program assets, including the requested regulatory assets, will be included in NIPSCO's rate base for ratemaking purposes in rate cases after the WAM assets have been placed in service. The hearing is scheduled for July 2024 with a final order expected in August 2024. Regulatory deferral related to renewable energy investments In accordance with the accounting principles of ASC 980, we recognize a regulatory liability or asset for amounts representing the timing difference between the profit earned from the JVs and the amount included in regulated rates to recover our approved investments in consolidated JVs. The amounts recorded in income will ultimately reflect the amount allowed in regulated rates to recover our investments over the useful life of the projects. The offset to the regulatory liability or asset associated with our renewable investments included in regulated rates is recorded in "Depreciation and amortization" on the Condensed Statements of Consolidated Income (unaudited). NiSource recorded an increase to depreciation expense of $3.5 million and a decrease to depreciation expense of $4.4 million for the three months ended March 31, 2024 and 2023, respectively. Following the implementation of the electric base rate case, we began recognizing amounts to recover our investments of projects that have been placed in service. Refer to Note 4, "Noncontrolling Interests," for additional information.

Fair Value

Fair Value	3 Months Ended
Fair Value	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value	A. Fair Value Measurements Recurring Fair Value Measurements The following tables present financial assets and liabilities measured and recorded at fair value on our Condensed Consolidated Balance Sheets (unaudited) on a recurring basis and their level within the fair value hierarchy as of March 31, 2024 and December 31, 2023: Recurring Fair Value Measurements (in millions) Quoted Prices in Significant Significant Balance as of March 31, 2024 Assets Risk management assets $ — $ 23.2 $ — $ 23.2 Available-for-sale debt securities — 150.1 — 150.1 Total $ — $ 173.3 $ — $ 173.3 Liabilities Risk management liabilities $ — $ 13.5 $ — $ 13.5 Total $ — $ 13.5 $ — $ 13.5 Recurring Fair Value Measurements (in millions) Quoted Prices in Significant Significant Balance as of December 31, 2023 Assets Risk management assets $ — $ 23.3 $ — $ 23.3 Available-for-sale debt securities — 159.1 — 159.1 Total $ — $ 182.4 $ — $ 182.4 Liabilities Risk management liabilities $ — $ 9.4 $ — $ 9.4 Total $ — $ 9.4 $ — $ 9.4 Risk Management Assets and Liabilities. Risk management assets and liabilities include exchange-traded NYMEX futures and NYMEX options and non-exchange-based forward purchase contracts. Level 1- When utilized, exchange-traded derivative contracts are based on unadjusted quoted prices in active markets and are classified within Level 1. These financial assets and liabilities are secured with cash on deposit with the exchange; therefore, nonperformance risk has not been incorporated into these valuations. These financial assets and liabilities are deemed to be cleared and settled daily by NYMEX as the related cash collateral is posted with the exchange. As a result of this exchange rule, NYMEX derivatives are considered to have no fair value at the balance sheet date for financial reporting purposes, and are presented in Level 1 net of posted cash; however, the derivatives remain outstanding and are subject to future commodity price fluctuations until they are settled in accordance with their contractual terms. Level 2- Certain non-exchange-traded derivatives are valued using broker or over-the-counter, on-line exchanges. In such cases, these non-exchange-traded derivatives are classified within Level 2. Non-exchange-based derivative instruments include swaps, forwards, and options. In certain instances, these instruments may utilize models to measure fair value. We use a similar model to value similar instruments. Valuation models utilize various inputs that include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, other observable inputs for the asset or liability and market-corroborated inputs, (i.e., inputs derived principally from or corroborated by observable market data by correlation or other means). Where observable inputs are available for substantially the full term of the asset or liability, the instrument is categorized within Level 2. Level 3- Certain derivatives trade in less active markets with a lower availability of pricing information and models may be utilized in the valuation. When such inputs have a significant impact on the measurement of fair value, the instrument is categorized within Level 3. Credit risk is considered in the fair value calculation of derivative instruments that are not exchange-traded. Credit exposures are adjusted to reflect collateral agreements that reduce exposures. As of March 31, 2024 and December 31, 2023, there were no material transfers between fair value hierarchies. Additionally, there were no changes in the method or significant assumptions used to estimate the fair value of our financial instruments. NIPSCO and Columbia of Pennsylvania have entered into long-term forward natural gas purchase instruments to lock in a fixed price for natural gas customers. We value these contracts using a pricing model that incorporates market-based information when available, as these instruments trade less frequently and are classified within Level 2 of the fair value hierarchy. For additional information, see Note 11, "Risk Management Activities." Available-for-Sale Debt Securities. Available-for-sale debt securities are investments pledged as collateral for trust accounts related to our wholly owned insurance company. We value U.S. Treasury, corporate debt and mortgage-backed securities using a matrix pricing model that incorporates market-based information. These securities trade less frequently and are classified within Level 2. Our available-for-sale debt securities impairments are recognized periodically using an allowance approach. At each reporting date, we utilize a quantitative and qualitative review process to assess the impairment of available-for-sale debt securities at the individual security level. For securities in a loss position, we evaluate our intent to sell or whether it is more-likely-than-not that we will be required to sell the security prior to the recovery of its amortized cost. If either criteria is met, the loss is recognized in earnings immediately, with the offsetting entry to the carrying value of the security. If both criteria are not met, we perform an analysis to determine whether the unrealized loss is related to credit factors. The analysis focuses on a variety of factors that include, but are not limited to, downgrade on ratings of the security, defaults in the current reporting period or projected defaults in the future, the security's yield spread over treasuries, and other relevant market data. If the unrealized loss is not related to credit factors, it is included in other comprehensive income. If the unrealized loss is related to credit factors, the loss is recognized as credit loss expense in earnings during the period, with an offsetting entry to the allowance for credit losses. The amount of the credit loss recorded to the allowance account is limited by the amount at which the security's fair value is less than its amortized cost basis. If certain amounts recorded in the allowance for credit losses are deemed uncollectible, the allowance on the uncollectible portion will be charged off, with an offsetting entry to the carrying value of the security. Subsequent improvements to the estimated credit losses of available-for-sale debt securities will be recognized immediately in earnings. As of March 31, 2024 and December 31, 2023, we have $0.4 million and $0.6 million, respectively, recorded as an allowance for credit losses on available-for-sale debt securities as a result of the analysis described above. Continuous credit monitoring and portfolio credit balancing mitigates our risk of credit losses on our available-for-sale debt securities. The amortized cost, gross unrealized gains and losses, allowance for credit losses, and fair value of available-for-sale securities at March 31, 2024 and December 31, 2023 were: March 31, 2024 (in millions) Amortized Gross Unrealized Gains Gross Unrealized Losses (1) Allowance for Credit Losses Fair Available-for-sale debt securities U.S. Treasury debt securities $ 62.1 $ — $ (3.3) $ — $ 58.8 Corporate/Other debt securities 98.1 0.6 (7.0) (0.4) 91.3 Total $ 160.2 $ 0.6 $ (10.3) $ (0.4) $ 150.1 December 31, 2023 (in millions) Amortized Gross Unrealized Gains Gross Unrealized Losses (2) Allowance for Credit Losses Fair Available-for-sale debt securities U.S. Treasury debt securities $ 63.8 $ — $ (3.2) $ — $ 60.6 Corporate/Other debt securities 105.2 0.8 (6.9) (0.6) 98.5 Total $ 169.0 $ 0.8 $ (10.1) $ (0.6) $ 159.1 (1) Fair value of U.S. Treasury debt securities and Corporate/Other debt securities in an unrealized loss position without an allowance for credit losses is $58.8 million and $72.7 million, respectively, at March 31, 2024. (2) Fair value of U.S. Treasury debt securities and Corporate/Other debt securities in an unrealized loss position without an allowance for credit losses is $58.7 million and $74.8 million, respectively, at December 31, 2023. The cost of maturities sold is based upon specific identification. Realized gains and losses on available-for-sale securities were $0.4 million and immaterial for the three months ended March 31, 2024 and 2023, respectively. Non-recurring Fair Value Measurements We measure the fair value of certain assets, primarily goodwill, on a non-recurring basis, typically when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. B. Other Fair Value Disclosures for Financial Instruments. The carrying amount of cash and cash equivalents, restricted cash, notes receivable, customer deposits and short-term borrowings is a reasonable estimate of fair value due to their liquid or short-term nature. Our long-term borrowings are recorded at historical amounts. The following method and assumptions were used to estimate the fair value of each class of financial instruments. Long-term Debt. The fair value of outstanding long-term debt is estimated based on the quoted market prices for the same or similar securities. Certain premium costs associated with the early settlement of long-term debt are not taken into consideration in determining fair value. These fair value measurements are classified within Level 2 of the fair value hierarchy. As of March 31, 2024, there was no change in the method or significant assumptions used to estimate the fair value of long-term debt. The carrying amount and estimated fair values of these financial instruments were as follows: (in millions) Carrying Amount as of March 31, 2024 Estimated Fair Value as of March 31, 2024 Carrying Amount as of Dec. 31, 2023 Estimated Fair Value as of Dec. 31, 2023 Long-term debt (including current portion) $ 11,748.6 $ 10,852.3 $ 11,079.3 $ 10,370.9

Income Taxes

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Our interim effective tax rates reflect the estimated annual effective tax rates for 2024 and 2023 applied to year-to-date pretax income, adjusted for tax expense associated with certain discrete items. The effective tax rates for the three months ended March 31, 2024 and 2023 were 16.0% and 20.3%, respectively. These effective tax rates differ from the federal statutory tax rate of 21% primarily due to renewable partnership income, amortization of excess deferred federal income tax liabilities, as specified in the TCJA, tax credits, state flow through, and other permanent book-to-tax differences. The decrease in the three month effective tax rate of 4.3% in 2024 compared to 2023 is primarily attributed to the lower renewable partnership income, jurisdictional mix of pre-tax book income, offset by lower amortization of excess deferred federal income tax liabilities. As of March 31, 2024, there have been no material changes to our unrecognized tax benefits or possible changes that could reasonably be expected to occur during the next twelve months. See Note 15 to the Company’s Consolidated Financial Statements in the Annual Report on Form 10-K for the year ended December 31, 2023, for a discussion of these unrecognized tax benefits.

Pension And Other Postretiremen

Pension And Other Postretirement Benefits	3 Months Ended
Pension And Other Postretirement Benefits	Mar. 31, 2024
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Pension And Other Postretirement Benefits	We provide defined contribution plans and noncontributory defined benefit retirement plans that cover certain of our employees. Benefits under the defined benefit retirement plans reflect the employees' compensation, years of service and age at retirement. Additionally, we provide health care and life insurance benefits for certain retired employees. The majority of employees may become eligible for these benefits if they reach retirement age while working for us. The expected cost of such benefits is accrued during the employees' years of service. We determined that, for certain rate-regulated subsidiaries, the future recovery of postretirement benefit costs is probable, and we record regulatory assets and liabilities for amounts that would otherwise have been recorded to expense or accumulated other comprehensive loss. Current rates of rate-regulated companies include postretirement benefit costs, including amortization of the regulatory assets and liabilities that arose prior to inclusion of these costs in rates. For most plans, cash contributions are remitted to grantor trusts. For the three months ended March 31, 2024 and 2023, we contributed $0.7 million and $1.2 million, respectively to our pension plans and $5.4 million and $5.6 million, respectively to our OPEB plans. The following table provides the components of the plans' actuarially determined net periodic benefit cost for the three months ended March 31, 2024 and 2023: Pension Benefits OPEB Three Months Ended March 31, (in millions) 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (1) Service cost $ 5.4 $ 5.1 $ 1.3 $ 1.3 Interest cost 16.3 17.1 5.4 5.4 Expected return on assets (23.8) (23.6) (4.0) (3.8) Amortization of prior service credit — — (0.4) (0.5) Recognized actuarial loss 7.2 8.4 0.8 0.8 Total Net Periodic Benefit Cost $ 5.1 $ 7.0 $ 3.1 $ 3.2 (1) The service cost component and all non-service cost components of net periodic benefit (income) cost are presented in "Operation and maintenance" and "Other, net," respectively, on the Condensed Statements of Consolidated Income (unaudited).

Variable Interest Entities

Variable Interest Entities	3 Months Ended
Variable Interest Entities	Mar. 31, 2024
Variable Interest Entities [Abstract]
Variable Interest Entities	A VIE is an entity in which the controlling interest is determined through means other than a majority voting interest. NIPSCO is a member of joint ventures that own and operate two wind facilities, Rosewater and Indiana Crossroads Wind, which have 102 MW and 302 MW of nameplate capacity, respectively. NIPSCO is also a member of joint ventures that own two solar facilities, Indiana Crossroads Solar and Dunns Bridge I, which have a combined 465 MW of nameplate capacity. We have determined that these joint ventures are VIEs. We control decisions that are significant to these entities' ongoing operations and economic results. Therefore, we have concluded that NIPSCO is the primary beneficiary and have consolidated all four entities. Members of each respective JV include NIPSCO (who is the managing member) and a tax equity partner. Earnings, tax attributes and cash flows are allocated to both NIPSCO and the tax equity partner in varying percentages by category and over the life of the partnership. NIPSCO and each tax equity partner contributed cash to each JV. Once the tax equity partner has earned their negotiated rate of return and have reached a stated contractual date, NIPSCO has the option to purchase the remaining interest in the respective JV, at fair market value from the tax equity partner. NIPSCO has an obligation to purchase 100% of the electricity generated by our commercially operational JVs. We did not provide any financial or other support during the quarter that was not previously contractually required, nor do we expect to provide such support in the future. Our Condensed Consolidated Balance Sheets (unaudited) included the following assets and liabilities associated with VIEs. (in millions) March 31, 2024 December 31, 2023 Net Property, Plant and Equipment $ 1,358.2 $ 1,369.8 Current assets 60.8 63.6 Total assets (1) 1,419.0 1,433.4 Current liabilities 60.9 68.3 Asset retirement obligations 56.3 55.7 Total liabilities (1)(2) $ 117.2 $ 124.0 (1) The assets of each VIE represent assets of a consolidated VIE that can be used only to settle obligations of the respective consolidated VIE. The creditors of the liabilities of the VIEs do not have recourse to the general credit of the primary beneficiary. (2) In addition to the amounts disclosed above there is a de minimis amount of other noncurrent liabilities at Rosewater as of March 31, 2024. Voting Interest Entities. In December 31, 2023, we consummated the NIPSCO Minority Interest Transaction for a capital contribution of $2.16 billion in cash. The difference between the $2.16 billion consideration received and the $1.36 billion carrying value of the noncontrolling interest claim on net assets was recorded to additional paid-in capital, net of $54.7 million

Long-Term Debt

Long-Term Debt	3 Months Ended
Long-Term Debt	Mar. 31, 2024
Long-Term Debt, Current and Noncurrent [Abstract]
Long-term Debt	On March 14, 2024 we completed the issuance and sale of $650.0 million of 5.35% senior unsecured notes maturing in 2034, which resulted in approximately $642.6 million of net proceeds after discount and debt issuance costs.

Short-Term Borrowings

Short-Term Borrowings	3 Months Ended
Short-Term Borrowings	Mar. 31, 2023
Short-Term Debt [Abstract]
Short-Term Borrowings	We generate short-term borrowings from our revolving credit facility, commercial paper program, accounts receivable transfer programs, and term credit agreements. Each of these borrowing sources is described further below. Revolving Credit Facility. We maintain a revolving credit facility to fund ongoing working capital requirements, including the provision of liquidity support for our commercial paper program, provide for issuance of letters of credit and also for general corporate purposes. Our revolving credit facility has a program limit of $1.85 billion and is comprised of a syndicate of banks. We had no outstanding borrowings under this facility as of March 31, 2024 and December 31, 2023. Commercial Paper Program. On February 9, 2024 we increased our commercial paper program limit from $1.50 billion to $1.85 billion. We had $1,222.3 million and $1,061.0 million of commercial paper outstanding with weighted-average interest rates of 5.58% and 5.65% as of March 31, 2024 and December 31, 2023, respectively. Accounts Receivable Transfer Programs. Columbia of Ohio, NIPSCO, and Columbia of Pennsylvania each maintain a receivables agreement whereby they transfer their customer accounts receivables to third-party financial institutions through consolidated special purpose entities. The three agreements expire between June 2024 and October 2024 and may be further extended if mutually agreed to by the parties thereto. All receivables transferred to third parties are valued at face value, which approximates fair value due to their short-term nature. The amount of the undivided percentage ownership interest in the accounts receivables transferred is determined in part by required loss reserves under the agreements. Transfers of accounts receivable are accounted for as secured borrowings resulting in the recognition of short-term borrowings on the Condensed Consolidated Balance Sheets (unaudited). As of March 31, 2024, the maximum amount of debt that could be borrowed related to our accounts receivable programs was $419.8 million. We had zero and $337.6 million of short-term borrowings related to the securitization transactions as of March 31, 2024 and December 31, 2023, respectively. For the three months ended March 31, 2024 and 2023, $337.6 million and $65.4 million, respectively were recorded as cash flows used for financing activities related to the change in short-term borrowings due to securitization transactions. For the accounts receivable transfer programs, we pay used facility fees for amounts borrowed, unused commitment fees for amounts not borrowed, and upfront renewal fees. Fees associated with the securitization transactions were $0.5 million and $0.9 million for the three months ended March 31, 2024 and 2023, respectively. Columbia of Ohio, NIPSCO and Columbia of Pennsylvania remain responsible for collecting on the receivables securitized, and the receivables cannot be transferred to another party. Term Credit Agreements. At December 31, 2023, we had $1.0 billion, and $650.0 million outstanding under term credit agreements with interest rates of 6.41% and 6.50%, respectively. On January 3, 2024, we terminated and repaid in full our $1.0 billion term credit agreement and our $650.0 million term credit agreement with proceeds from the NIPSCO Minority Interest Transaction. Items listed above, excluding the term credit agreements, are presented net in the Condensed Statements of Consolidated Cash Flows (unaudited) as their maturities are less than 90 days.

Other Commitments And Contingen

Other Commitments And Contingencies	3 Months Ended
Other Commitments And Contingencies	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Guarantees and Indemnities. We and certain of our subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of certain subsidiaries as a part of normal business. Such agreements include guarantees and stand-by letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the subsidiaries' intended commercial purposes. As of March 31, 2024 and December 31, 2023, we had issued stand-by letters of credit of $9.9 million for the benefit of third parties. We provide guarantees related to our future performance under BTAs for our renewable generation projects. At March 31, 2024 and December 31, 2023, our guarantees for multiple BTAs totaled $672.3 million and $646.1 million, respectively. The amount of each guaranty will decrease upon the substantial completion of the construction of the facilities. See ''- D. Other Matters - Generation Transition,'' below for more information. B. Legal Proceedings. From time to time, various legal and regulatory claims and proceedings are pending or threatened against the Company and its subsidiaries. While the amounts claimed may be substantial, the Company is unable to predict with certainty the ultimate outcome of such claims and proceedings. The Company establishes reserves whenever it believes it to be appropriate for pending litigation matters. However, the actual results of resolving the pending litigation matters may be substantially higher than the amounts reserved. If one or more matters were decided against us, the effects could be material to our results of operations in the period in which we would be required to record or adjust the related liability and could also be material to our cash flows in the periods that we would be required to pay such liability. Due to the inherent uncertainty of litigation, there can be no assurance that the resolution of any particular claim, proceeding or investigation would not have a material adverse effect on our results of operations, financial position or liquidity. Other Claims and Proceedings. We are also party to other claims, regulatory and legal proceedings arising in the ordinary course of business in each state in which we have operations, and based upon an investigation of these matters and discussion with legal counsel, we believe the ultimate outcome of such other legal proceedings to be individually, or in aggregate, not material at this time. Our operations are subject to environmental statutes and regulations related to air quality, water quality, hazardous waste and solid waste. We believe that we are in substantial compliance with the environmental regulations currently applicable to our operations. It is management's continued intent to address environmental issues in cooperation with regulatory authorities in such a manner as to achieve mutually acceptable compliance plans. However, there can be no assurance that fines and penalties will not be incurred. Management expects a majority of environmental assessment and remediation costs and asset retirement costs, further described below, to be recoverable through rates. As of March 31, 2024 and December 31, 2023, we had recorded a liability of $77.8 million and $80.0 million, respectively, to cover environmental remediation at various sites. This liability is included in "Other accruals" and "Other noncurrent liabilities and deferred credits" in the Condensed Consolidated Balance Sheets (unaudited). We recognize costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated. The original estimates for remediation activities may differ materially from the amount ultimately expended. The actual future expenditures depend on many factors, including laws and regulations, the nature and extent of impact and the method of remediation. These expenditures are not currently estimable at some sites. We periodically adjust our liability as information is collected and estimates become more refined. CERCLA. Our subsidiaries are potentially responsible parties at waste disposal sites under CERCLA and similar state laws. Under CERCLA, each potentially responsible party can be held jointly, severally and strictly liable for the remediation costs as the EPA, or state, can allow the parties to pay for remedial action or perform remedial action themselves and request reimbursement from the potentially responsible parties. Our affiliates have retained CERCLA environmental liabilities, including remediation liabilities, associated with certain current and former operations. At this time, we cannot estimate the full cost of remediating properties that have not yet been investigated, but it is possible that the future costs could be material to the Condensed Consolidated Financial Statements (unaudited). MGP. We maintain a program to identify and investigate former MGP sites where our subsidiaries or predecessors may have liability. The program has identified 53 such sites where liability is probable. Remedial actions at many of these sites are being overseen by state or federal environmental agencies through consent agreements or voluntary remediation agreements. We utilize a probabilistic model to estimate our future remediation costs related to MGP sites. The model was prepared with the assistance of a third party and incorporates our experience and general industry experience with remediating MGP sites. We complete an annual refresh of the model in the second quarter of each fiscal year. Our total estimated liability related to the facilities subject to remediation was $72.8 million and $73.7 million at March 31, 2024 and December 31, 2023, respectively. The liability represents our best estimate of the probable cost to remediate the MGP sites. Our model indicates that it is reasonably possible that remediation costs could vary by as much as $15.1 million in addition to the costs noted above. Remediation costs are estimated based on the best available information, applicable remediation standards at the balance sheet date and experience with similar facilities. CCRs. NIPSCO continues to meet the compliance requirements established by the EPA for the regulation of CCRs. The CCR rule requirements currently in effect required revisions to previously recorded legal obligations associated with the retirement of certain NIPSCO facilities. The actual asset retirement costs related to the CCR rule may vary substantially from the estimates used to record the increased asset retirement obligation due to the uncertainty about the requirements that will be established by environmental authorities, compliance strategies that will be used and the preliminary nature of available data used to estimate costs. As allowed by the rule, NIPSCO will continue to collect data over time to determine the specific compliance solutions and associated costs and, as a result, the actual costs may vary. On April 25, 2024 new EPA rules have been issued and we are evaluating the potential impact on our business. Generation Transition.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	3 Months Ended
Accumulated Other Comprehensive Loss	Mar. 31, 2024
Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated Other Comprehensive Loss	The following tables display the components of Accumulated Other Comprehensive Loss, net of tax: (in millions) Gains and Losses on Securities (1) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2024 $ (7.3) $ (12.8) $ (13.5) $ (33.6) Other comprehensive loss before reclassifications (0.6) (0.2) (0.1) (0.9) Amounts reclassified from accumulated other comprehensive loss 0.3 0.1 0.3 0.7 Net current-period other comprehensive income (loss) (0.3) (0.1) 0.2 (0.2) Balance as of March 31, 2024 $ (7.6) $ (12.9) $ (13.3) $ (33.8) (1) All amounts are net of tax. Amounts in parentheses indicate debits. (in millions) Gains and Losses on Securities (1) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2023 $ (11.2) $ (12.6) $ (13.3) $ (37.1) Other comprehensive income (loss) before reclassifications 1.7 — — 1.7 Amounts reclassified from accumulated other comprehensive loss 0.3 0.1 0.3 0.7 Net current-period other comprehensive income (loss) 2.0 0.1 0.3 2.4 Balance as of March 31, 2023 $ (9.2) $ (12.5) $ (13.0) $ (34.7) (1) All amounts are net of tax. Amounts in parentheses indicate debits.

Other, Net

Other, Net	3 Months Ended
Other, Net	Mar. 31, 2024
Other, Net [Abstract]
Other, Net	Three Months Ended (in millions) 2024 2023 Interest income $ 2.5 $ 1.8 AFUDC equity 11.3 4.8 Pension and other postretirement non-service benefit (cost) (2.2) (3.5) Miscellaneous (2.4) (1.6) Total Other, net $ 9.2 $ 1.5

Accounting Changes and Error Co

Accounting Changes and Error Corrections (Policies)	3 Months Ended
Accounting Changes and Error Corrections (Policies)	Mar. 31, 2024
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements, Policy	Recently Issued Accounting Pronouncements In August 2023, the Financial Accounting Standards Board ("FASB") issued ASU 2023-05, Business Combinations- Joint Venture Formations. This pronouncement codifies ASU 805-60 to provide guidance for the recognition and initial measurement of joint venture formations. This guidance requires that the initial assets contributed and liabilities assumed be recognized and measured at fair value, with additional disclosure requirements during the period a joint venture is formed. The pronouncement is effective for joint ventures formed on or after January 1, 2025. We will adopt and apply to any future joint ventures if entered. In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This pronouncement enhances annual and interim disclosure requirements over reportable segments, primarily through enhanced disclosures about significant segment expenses that are regularly provided to or easily computed from information regularly provided to the chief operating decision maker ("CODM") and included within each reported measure of segment profit or loss. The pronouncement also allows for more than one measure of segment profit if the CODM uses more than one measure in assessing segment performance. The pronouncement is effective for annual periods beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. We are currently evaluating the impacts this ASU will have on our disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This pronouncement enhances required income tax disclosures. The pronouncement will require disclosure of specific categories and reconciling items included in the rate reconciliation, disaggregation between federal, state and local income taxes paid, and disclosure of income taxes paid by jurisdictions over a certain threshold. Additionally, the pronouncement eliminates certain required disclosures related to unrecognized tax benefits. This ASU is effective for annual periods beginning after December 15, 2024, with early adoption permitted, and is to be applied on a prospective basis with retrospective application permitted. We are currently evaluating the impacts this amendment will have on our income tax disclosures, but do not expect to early adopt.

Revenue Recognition (Tables)

Revenue Recognition (Tables)	3 Months Ended
Revenue Recognition (Tables)	Mar. 31, 2024
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The tables below reconcile revenue disaggregation by customer class to segment revenue, as well as to revenues reflected on the Condensed Statements of Consolidated Income (unaudited): Three months ended March 31, 2024 (in millions) Columbia Operations NIPSCO Operations Corporate and Other Total Gas Distribution Residential $ 628.0 $ 212.1 $ — $ 840.1 Commercial 220.4 74.7 — 295.1 Industrial 40.1 23.8 — 63.9 Off-system 12.8 — — 12.8 Wholesale 0.8 — — 0.8 Miscellaneous (1) 8.2 7.9 — 16.1 Subtotal $ 910.3 $ 318.5 $ — $ 1,228.8 Electric Generation and Power Delivery Residential $ — $ 143.8 $ — $ 143.8 Commercial — 142.9 — 142.9 Industrial — 115.9 — 115.9 Wholesale — 6.3 — 6.3 Public Authority — 2.1 — 2.1 Miscellaneous (1) — 3.2 — 3.2 Subtotal $ — $ 414.2 $ — $ 414.2 Total Customer Revenues (2) 910.3 732.7 — 1,643.0 Other Revenues (3) 43.4 19.7 0.2 63.3 Total Operating Revenues $ 953.7 $ 752.4 $ 0.2 $ 1,706.3 (1) Amounts included in Columbia Operations are primarily related to earnings share mechanisms and late fees. Amounts included in NIPSCO Operations are primarily related to revenue refunds, public repairs and property rentals. (2) Customer revenue amounts exclude intersegment revenues. See Note 17, "Business Segment Information," for discussion of intersegment revenues. (3) Amounts included in Columbia Operations primarily relate to weather normalization adjustment mechanisms. Amounts included in NIPSCO Operations primarily relate to MISO multi-value projects and revenue from non-jurisdictional transmission assets. Three months ended March 31, 2023 (in millions) Columbia Operations NIPSCO Operations Corporate and Other Total Gas Distribution Residential $ 684.6 $ 302.4 $ — $ 987.0 Commercial 248.0 112.6 — 360.6 Industrial 40.4 31.5 — 71.9 Off-system 17.2 — — 17.2 Wholesale 1.0 — — 1.0 Miscellaneous (1) 11.8 5.6 — 17.4 Subtotal $ 1,003.0 $ 452.1 $ — $ 1,455.1 Electric Generation and Power Delivery Residential $ — $ 150.4 $ — $ 150.4 Commercial — 150.9 — 150.9 Industrial — 134.2 — 134.2 Wholesale — 2.6 — 2.6 Public Authority — 2.1 — 2.1 Miscellaneous (1) — 0.8 — 0.8 Subtotal $ — $ 441.0 $ — $ 441.0 Total Customer Revenues (2) 1,003.0 893.1 — 1,896.1 Other Revenues (3) 45.9 23.8 0.2 69.9 Total Operating Revenues $ 1,048.9 $ 916.9 $ 0.2 $ 1,966.0 (1) Amounts included in Columbia Operations are primarily related to earnings share mechanisms and late fees. Amounts included in NIPSCO Operations, are primarily related to revenue refunds, public repairs and property rentals. (2) Customer revenue amounts exclude intersegment revenues. See Note 17, "Business Segment Information," for discussion of intersegment revenues. (3) Amounts included in Columbia Operations are primarily relate to weather normalization adjustment mechanisms. Amounts included in NIPSCO Operations primarily relate to MISO multi-value projects and revenue from non-jurisdictional transmission assets.
Customer Accounts Receivable	The opening and closing balances of customer receivables for the three months ended March 31, 2024 are presented in the table below. We had no significant contract assets or liabilities during the period. Additionally, we have not incurred any significant costs to obtain or fulfill contracts. (in millions) Customer Accounts Receivable, Billed (less reserve) Customer Accounts Receivable, Unbilled (less reserve) Balance as of December 31, 2023 $ 479.4 $ 337.6 Balance as of March 31, 2024 552.1 263.6
Accounts Receivable, Allowance for Credit Loss	A rollforward of our allowance for credit losses as of March 31, 2024 and December 31, 2023 are presented in the table below: ( in millions ) Columbia Operations NIPSCO Operations Corporate and Other Total Balance as of January 1, 2024 $ 10.2 $ 11.9 $ 0.8 $ 22.9 Current period provisions 11.0 3.6 — 14.6 Write-offs charged against allowance (7.3) (2.1) (0.8) (10.2) Recoveries of amounts previously written off 4.1 0.2 — 4.3 Balance as of March 31, 2024 $ 18.0 $ 13.6 $ — $ 31.6 ( in millions ) Columbia Operations NIPSCO Operations Corporate and Other Total Balance as of January 1, 2023 $ 11.1 $ 12.0 $ 0.8 $ 23.9 Current period provisions 28.3 11.5 — 39.8 Write-offs charged against allowance (49.2) (12.4) — (61.6) Recoveries of amounts previously written off 20.0 0.8 — 20.8 Balance as of December 31, 2023 $ 10.2 $ 11.9 $ 0.8 $ 22.9

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
Earnings Per Share (Tables)	Mar. 31, 2024
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table presents the calculation of our basic and diluted EPS: Three Months Ended (in millions, except per share amounts) 2024 2023 Numerator: Net Income Available to Common Shareholders $ 344.3 $ 319.2 Less: Income allocated to participating securities 0.3 0.2 Net Income Available to Common Shareholders - Basic 344.0 319.0 Add: Dilutive effect of Equity Units — 0.4 Net Income Available to Common Shareholders - Diluted $ 344.0 $ 319.4 Denominator: Average common shares outstanding - Basic 447.9 412.8 Dilutive potential common shares: Equity Units purchase contracts — 31.2 Equity Units purchase contract payment balance — 1.8 Shares contingently issuable under employee stock plans 0.9 0.8 Shares restricted under employee stock plans 0.4 0.5 ATM forward agreement 0.2 — Average Common Shares - Diluted 449.4 447.1 Earnings per common share: Basic 0.77 0.77 Diluted 0.77 0.71

Equity (Tables)

Equity (Tables)	3 Months Ended
Equity (Tables)	Mar. 31, 2024
Equity [Abstract]
Schedule of Stock by Class - Preferred	On June 15, 2023, we redeemed all 400,000 outstanding shares of Series A Preferred Stock for a redemption price of $1,000 per share or $400.0 million in total.

Risk Management Activities (Tab

Risk Management Activities (Tables)	3 Months Ended
Risk Management Activities (Tables)	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	Risk management assets and liabilities on our derivatives are presented on the Condensed Consolidated Balance Sheets (unaudited) as shown below: March 31, 2024 December 31, 2023 (in millions) Assets Liabilities Assets Liabilities Current (1) Derivatives not designated as hedging instruments $ 3.0 $ 11.6 $ 1.1 $ 7.5 Total $ 3.0 $ 11.6 $ 1.1 $ 7.5 Noncurrent (2) Derivatives not designated as hedging instruments $ 20.2 $ 1.9 $ 22.2 $ 1.9 Total $ 20.2 $ 1.9 $ 22.2 $ 1.9 (1) Current assets and liabilities are presented in "Prepayments and other" and "Other accruals", respectively, on the Condensed Consolidated Balance Sheets (unaudited). (2) Noncurrent assets and liabilities are presented in "Deferred charges and other" and "Other noncurrent liabilities and deferred credits", respectively, on the Condensed Consolidated Balance Sheets (unaudited).
Derivative Instruments, Gain (Loss)	The following table summarizes the gains and losses associated with the commodity price risk programs deferred as regulatory assets and liabilities: (in millions) March 31, 2024 December 31, 2023 Regulatory Assets Losses on commodity price risk programs $ 20.1 $ 24.4 Regulatory Liabilities Gains on commodity price risk programs 23.3 23.3

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
Fair Value (Tables)	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables present financial assets and liabilities measured and recorded at fair value on our Condensed Consolidated Balance Sheets (unaudited) on a recurring basis and their level within the fair value hierarchy as of March 31, 2024 and December 31, 2023: Recurring Fair Value Measurements (in millions) Quoted Prices in Significant Significant Balance as of March 31, 2024 Assets Risk management assets $ — $ 23.2 $ — $ 23.2 Available-for-sale debt securities — 150.1 — 150.1 Total $ — $ 173.3 $ — $ 173.3 Liabilities Risk management liabilities $ — $ 13.5 $ — $ 13.5 Total $ — $ 13.5 $ — $ 13.5 Recurring Fair Value Measurements (in millions) Quoted Prices in Significant Significant Balance as of December 31, 2023 Assets Risk management assets $ — $ 23.3 $ — $ 23.3 Available-for-sale debt securities — 159.1 — 159.1 Total $ — $ 182.4 $ — $ 182.4 Liabilities Risk management liabilities $ — $ 9.4 $ — $ 9.4 Total $ — $ 9.4 $ — $ 9.4
Debt Securities, Available-for-sale	The amortized cost, gross unrealized gains and losses, allowance for credit losses, and fair value of available-for-sale securities at March 31, 2024 and December 31, 2023 were: March 31, 2024 (in millions) Amortized Gross Unrealized Gains Gross Unrealized Losses (1) Allowance for Credit Losses Fair Available-for-sale debt securities U.S. Treasury debt securities $ 62.1 $ — $ (3.3) $ — $ 58.8 Corporate/Other debt securities 98.1 0.6 (7.0) (0.4) 91.3 Total $ 160.2 $ 0.6 $ (10.3) $ (0.4) $ 150.1 December 31, 2023 (in millions) Amortized Gross Unrealized Gains Gross Unrealized Losses (2) Allowance for Credit Losses Fair Available-for-sale debt securities U.S. Treasury debt securities $ 63.8 $ — $ (3.2) $ — $ 60.6 Corporate/Other debt securities 105.2 0.8 (6.9) (0.6) 98.5 Total $ 169.0 $ 0.8 $ (10.1) $ (0.6) $ 159.1 (1) Fair value of U.S. Treasury debt securities and Corporate/Other debt securities in an unrealized loss position without an allowance for credit losses is $58.8 million and $72.7 million, respectively, at March 31, 2024. (2) Fair value of U.S. Treasury debt securities and Corporate/Other debt securities in an unrealized loss position without an allowance for credit losses is $58.7 million and $74.8 million, respectively, at December 31, 2023.
Carrying Amount And Estimated Fair Values Of Financial Instruments	The carrying amount and estimated fair values of these financial instruments were as follows: (in millions) Carrying Amount as of March 31, 2024 Estimated Fair Value as of March 31, 2024 Carrying Amount as of Dec. 31, 2023 Estimated Fair Value as of Dec. 31, 2023 Long-term debt (including current portion) $ 11,748.6 $ 10,852.3 $ 11,079.3 $ 10,370.9

Pension And Other Postretirem_2

Pension And Other Postretirement Benefits (Tables)	3 Months Ended
Pension And Other Postretirement Benefits (Tables)	Mar. 31, 2024
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Components Of The Plans' Net Periodic Benefits Cost	The following table provides the components of the plans' actuarially determined net periodic benefit cost for the three months ended March 31, 2024 and 2023: Pension Benefits OPEB Three Months Ended March 31, (in millions) 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (1) Service cost $ 5.4 $ 5.1 $ 1.3 $ 1.3 Interest cost 16.3 17.1 5.4 5.4 Expected return on assets (23.8) (23.6) (4.0) (3.8) Amortization of prior service credit — — (0.4) (0.5) Recognized actuarial loss 7.2 8.4 0.8 0.8 Total Net Periodic Benefit Cost $ 5.1 $ 7.0 $ 3.1 $ 3.2 (1) The service cost component and all non-service cost components of net periodic benefit (income) cost are presented in "Operation and maintenance" and "Other, net," respectively, on the Condensed Statements of Consolidated Income (unaudited).

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	3 Months Ended
Variable Interest Entities (Tables)	Mar. 31, 2024
Variable Interest Entities [Abstract]
Variable Interest Entities Assets and Liabilities	Our Condensed Consolidated Balance Sheets (unaudited) included the following assets and liabilities associated with VIEs. (in millions) March 31, 2024 December 31, 2023 Net Property, Plant and Equipment $ 1,358.2 $ 1,369.8 Current assets 60.8 63.6 Total assets (1) 1,419.0 1,433.4 Current liabilities 60.9 68.3 Asset retirement obligations 56.3 55.7 Total liabilities (1)(2) $ 117.2 $ 124.0

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
Accumulated Other Comprehensive Loss (Tables)	Mar. 31, 2024
Other Comprehensive Income (Loss), Tax [Abstract]
Components Of Accumulated Other Comprehensive Loss	The following tables display the components of Accumulated Other Comprehensive Loss, net of tax: (in millions) Gains and Losses on Securities (1) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2024 $ (7.3) $ (12.8) $ (13.5) $ (33.6) Other comprehensive loss before reclassifications (0.6) (0.2) (0.1) (0.9) Amounts reclassified from accumulated other comprehensive loss 0.3 0.1 0.3 0.7 Net current-period other comprehensive income (loss) (0.3) (0.1) 0.2 (0.2) Balance as of March 31, 2024 $ (7.6) $ (12.9) $ (13.3) $ (33.8) (1) All amounts are net of tax. Amounts in parentheses indicate debits. (in millions) Gains and Losses on Securities (1) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2023 $ (11.2) $ (12.6) $ (13.3) $ (37.1) Other comprehensive income (loss) before reclassifications 1.7 — — 1.7 Amounts reclassified from accumulated other comprehensive loss 0.3 0.1 0.3 0.7 Net current-period other comprehensive income (loss) 2.0 0.1 0.3 2.4 Balance as of March 31, 2023 $ (9.2) $ (12.5) $ (13.0) $ (34.7) (1) All amounts are net of tax. Amounts in parentheses indicate debits.

Other, Net (Tables)

Other, Net (Tables)	3 Months Ended
Other, Net (Tables)	Mar. 31, 2024
Other, Net [Abstract]
Schedule of Other Nonoperating Income (Expense)	Three Months Ended (in millions) 2024 2023 Interest income $ 2.5 $ 1.8 AFUDC equity 11.3 4.8 Pension and other postretirement non-service benefit (cost) (2.2) (3.5) Miscellaneous (2.4) (1.6) Total Other, net $ 9.2 $ 1.5

Business Segment Information (T

Business Segment Information (Tables)	3 Months Ended
Business Segment Information (Tables)	Mar. 31, 2024
Segment Reporting [Abstract]
Schedule Of Operating Income Derived From Revenues And Expenses By Segment	Three Months Ended (in millions) 2024 2023 Operating Revenues Columbia Operations Unaffiliated $ 953.7 $ 1,048.9 Intersegment 3.2 3.0 Total 956.9 1,051.9 NIPSCO Operations Unaffiliated 752.4 916.9 Intersegment 0.3 0.3 Total 752.7 917.2 Corporate and Other Unaffiliated 0.2 0.2 Intersegment 139.9 116.7 Total 140.1 116.9 Eliminations (143.4) (120.0) Consolidated Operating Revenues $ 1,706.3 $ 1,966.0 Operating Income Columbia Operations $ 362.0 $ 351.8 NIPSCO Operations 216.4 177.0 Corporate and Other 5.0 2.2 Consolidated Operating Income $ 583.4 $ 531.0 The following table provides information about the assets of our reportable segments included in the Condensed Consolidated Balance Sheet (unaudited): (in millions) March 31, December 31, Assets Columbia Operations $ 13,789.8 $ 13,664.5 NIPSCO Operations 14,221.0 13,962.6 Corporate and Other 1,327.3 3,450.1 Consolidated Assets $ 29,338.1 $ 31,077.2 Information about our reportable segments for the three months ended March 31, 2023, as well as for the period ended December 31, 2023 has been recast to align with the current year's presentation.

Revenue Recognition (Narrative)

Revenue Recognition (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Accounts Receivable, Allowance for Credit Loss	$ 31.6	$ 22.9	$ 23.9
Current period provisions	14.6	39.8
Write-offs charged against allowance	(10.2)	(61.6)
Recoveries of amounts previously written off	$ 4.3	$ 20.8

Revenue Recognition (Disaggrega

Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Customer revenues	$ 1,643	$ 1,896.1
Other revenues	63.3	69.9
Total Operating Revenues	1,706.3	1,966
Revenues	1,706.3	1,966
NiSource Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	1,228.8	1,455.1
NiSource Electric Generation and Power Delivery
Disaggregation of Revenue [Line Items]
Customer revenues	414.2	441
Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Other revenues	0.2	0.2
Revenues	140.1	116.9
Corporate and Other \| Unaffiliated
Disaggregation of Revenue [Line Items]
Revenues	0.2	0.2
NIPSCO Operations
Disaggregation of Revenue [Line Items]
Customer revenues	732.7	893.1
Other revenues	19.7	23.8
Total Operating Revenues	752.4
Revenues	752.7	917.2
NIPSCO Operations \| Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	318.5	452.1
NIPSCO Operations \| NIPSCO Electric Generation
Disaggregation of Revenue [Line Items]
Customer revenues	414.2	441
NIPSCO Operations \| Unaffiliated
Disaggregation of Revenue [Line Items]
Revenues	752.4	916.9
Columbia Operations
Disaggregation of Revenue [Line Items]
Customer revenues	910.3	1,003
Other revenues	43.4	45.9
Revenues	956.9	1,051.9
Columbia Operations \| Unaffiliated
Disaggregation of Revenue [Line Items]
Revenues	953.7	1,048.9
Residential \| NiSource Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	840.1	987
Residential \| NiSource Electric Generation and Power Delivery
Disaggregation of Revenue [Line Items]
Customer revenues	143.8	150.4
Residential \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Residential \| NIPSCO Operations \| Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	212.1	302.4
Residential \| NIPSCO Operations \| NIPSCO Electric Generation
Disaggregation of Revenue [Line Items]
Customer revenues	143.8	150.4
Residential \| Columbia Operations
Disaggregation of Revenue [Line Items]
Customer revenues	628	684.6
Commercial \| NiSource Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	295.1	360.6
Commercial \| NiSource Electric Generation and Power Delivery
Disaggregation of Revenue [Line Items]
Customer revenues	142.9	150.9
Commercial \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Commercial \| NIPSCO Operations \| Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	74.7	112.6
Commercial \| NIPSCO Operations \| NIPSCO Electric Generation
Disaggregation of Revenue [Line Items]
Customer revenues	142.9	150.9
Commercial \| Columbia Operations
Disaggregation of Revenue [Line Items]
Customer revenues	220.4	248
Industrial \| NiSource Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	63.9	71.9
Industrial \| NiSource Electric Generation and Power Delivery
Disaggregation of Revenue [Line Items]
Customer revenues	115.9	134.2
Industrial \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Industrial \| NIPSCO Operations \| Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	23.8	31.5
Industrial \| NIPSCO Operations \| NIPSCO Electric Generation
Disaggregation of Revenue [Line Items]
Customer revenues	115.9	134.2
Industrial \| Columbia Operations
Disaggregation of Revenue [Line Items]
Customer revenues	40.1	40.4
Off-system \| NiSource Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	12.8	17.2
Off-system \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Off-system \| NIPSCO Operations \| Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Off-system \| Columbia Operations
Disaggregation of Revenue [Line Items]
Customer revenues	12.8	17.2
Miscellaneous \| NiSource Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	16.1	17.4
Miscellaneous \| NiSource Electric Generation and Power Delivery
Disaggregation of Revenue [Line Items]
Customer revenues	3.2	0.8
Miscellaneous \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Miscellaneous \| NIPSCO Operations \| Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	7.9	5.6
Miscellaneous \| NIPSCO Operations \| NIPSCO Electric Generation
Disaggregation of Revenue [Line Items]
Customer revenues	3.2	0.8
Miscellaneous \| Columbia Operations
Disaggregation of Revenue [Line Items]
Customer revenues	8.2	11.8
Wholesale \| NiSource Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	0.8	1
Wholesale \| NiSource Electric Generation and Power Delivery
Disaggregation of Revenue [Line Items]
Customer revenues	6.3	2.6
Wholesale \| Corporate and Other
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Wholesale \| NIPSCO Operations \| Gas Distribution
Disaggregation of Revenue [Line Items]
Customer revenues	0	0
Wholesale \| NIPSCO Operations \| NIPSCO Electric Generation
Disaggregation of Revenue [Line Items]
Customer revenues	6.3	2.6
Wholesale \| Columbia Operations
Disaggregation of Revenue [Line Items]
Customer revenues	0.8	1
Public Authority
Disaggregation of Revenue [Line Items]
Customer revenues	2.1	2.1
Public Authority \| NIPSCO Operations \| NIPSCO Electric Generation
Disaggregation of Revenue [Line Items]
Customer revenues	$ 2.1	$ 2.1

Revenue Recognition (Customer A

Revenue Recognition (Customer Accounts Receivable) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Customer Accounts Receivable, Billed (Less Reserve)	$ 552.1	$ 479.4
Customer Accounts Receivable, Unbilled (Less Reserve)	$ 263.6	$ 337.6

Revenue Recognition Revenue Rec

Revenue Recognition Revenue Recognition (Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Accounts Receivable Allowance For Credit Loss [Line Items]
Accounts Receivable, Allowance for Credit Loss	$ 31.6		$ 22.9	$ 23.9
Current period provisions	14.6		39.8
Write-offs charged against allowance	10.2		61.6
Recoveries of amounts previously written off	4.3		20.8
Corporate and Other
Accounts Receivable Allowance For Credit Loss [Line Items]
Accounts Receivable, Allowance for Credit Loss	0		0.8	0.8
Current period provisions	0	$ 0
Write-offs charged against allowance	(0.8)	0
Recoveries of amounts previously written off	0	0
Columbia Operations
Accounts Receivable Allowance For Credit Loss [Line Items]
Accounts Receivable, Allowance for Credit Loss	18		10.2	11.1
Current period provisions	11	28.3
Write-offs charged against allowance	7.3	49.2
Recoveries of amounts previously written off	4.1	20
NIPSCO Operations
Accounts Receivable Allowance For Credit Loss [Line Items]
Accounts Receivable, Allowance for Credit Loss	13.6		$ 11.9	$ 12
Current period provisions	3.6	11.5
Write-offs charged against allowance	2.1	12.4
Recoveries of amounts previously written off	$ 0.2	$ 0.8

Earnings Per Share (Schedule of

Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator
Net Income Available to Common Shareholders	$ 344.3	$ 319.2
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	0.3	0.2
Net Income Available to Common Shareholders - Basic Excluding Participating Securities	344	319
Add: Dilutive effect of Equity Units	0	0.4
Net Income Available to Common Shareholders - Diluted	$ 344	$ 319.4
Denominator
Basic Average Common Shares Outstanding	447.9	412.8
Dilutive potential common shares
Equity Units purchase contracts		31.2
Equity Units purchase contract payment balance	0	1.8
Shares contingently issuable under employee stock plans	0.9	0.8
Shares restricted under stock plans	0.4	0.5
ATM forward agreement	0.2	0
Diluted Average Common Shares	449.4	447.1
Basic Earnings Per Share	$ 0.77	$ 0.77
Diluted Earnings Per Share	$ 0.77	$ 0.71

Equity (Narrative) (Details)

Equity (Narrative) (Details) - USD ($)		3 Months Ended		12 Months Ended
Equity (Narrative) (Details) - USD ($)	Feb. 22, 2024	Mar. 31, 2024	Mar. 31, 2023	Feb. 23, 2024	Mar. 15, 2024	Dec. 31, 2023	Dec. 01, 2023	Jun. 15, 2023
Preferred Stock, Shares Authorized		20,000,000				20,000,000
Preferred Stock, Shares Outstanding		0				40,000
Preferred Stock, Par or Stated Value Per Share		$ 0.01			$ 25,000	$ 0.01	$ 0.01
Preferred Stock Shares Redeemed		0
Common Stock, Shares, Issued							33,898,837
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share		$ 25.76		$ 25.78
Preferred Stock, Liquidation Preference Per Share								$ 1,000
Preferred Stock Redemption Premium		$ 14,000,000	$ 0
Pension Plan
Defined Benefit Plan, Plan Assets, Contributions by Employer		700,000	1,200,000
Other Postretirement Benefit Plan
Defined Benefit Plan, Plan Assets, Contributions by Employer		5,400,000	$ 5,600,000
At The Market Program
Common Stock Aggregate Sale Price	$ 900,000,000	199,800,000
ATM Program Equity Remaining Available for Issuance		$ 700
Forward February 23
Forward Contract Indexed to Issuer's Equity, Shares				7,757,951
Series A Preferred Stock
Preferred Stock, Shares Outstanding								400,000
Preferred Stock, Redemption Amount								$ 400,000,000
Preferred Stock, Dividends Per Share, Declared		$ 0	$ 28.25
Series B Preferred Stock
Preferred Stock, Dividends Per Share, Declared		$ 406.25	$ 812.50
Preferred Stock Redemption Premium		$ 14,000,000
Series B-1 Preferred Stock
Preferred Stock, Par or Stated Value Per Share					$ 0.01
Preferred Stock, Redemption Amount					$ 500,000,000
Preferred Stock, Shares Issued		20,000			20,000

Equity Schedule of Stock by Cla

Equity Schedule of Stock by Class - Preferred (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 15, 2024	Dec. 31, 2023	Jun. 15, 2023
Class of Stock [Line Items]
Preferred Stock, Liquidation Preference Per Share					$ 1,000
Preferred Stock, Shares Outstanding	0			40,000
Shares outstanding	$ 7,895.9			$ 8,269.6
Preferred Stock Shares Redeemed	0
Series A Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding					400,000
Dividends Declared Per Share	$ 0	$ 28.25
Preferred Stock, Redemption Amount					$ 400
Preferred Stock, Redemption Amount					$ 400
Series B Preferred Stock
Class of Stock [Line Items]
Dividends Declared Per Share	$ 406.25	$ 812.50
Series B-1 Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Redemption Amount			$ 500
Preferred Stock, Redemption Amount			$ 500
Preferred Stock
Class of Stock [Line Items]
Preferred Stock Shares Redeemed	(40,000)

Equity Schedule of Series A Equ

Equity Schedule of Series A Equity Units (Details) - $ / shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Series A Preferred Stock
Schedule of Series A Equity Units [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 28.25
Series B Preferred Stock
Schedule of Series A Equity Units [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 406.25	$ 812.50

Gas in Storage (Narrative) (Det

Gas in Storage (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Gas in Storage [Abstract]
LIFO Inventory Amount	$ 27.5	$ 0
Inventory [Line Items]
LIFO Inventory Amount	$ 27.5	$ 0

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Public Utilities, General Disclosures [Line Items]
Depreciation, Nonproduction	$ 3.5	$ 4.4

Risk Management Activities (Nar

Risk Management Activities (Narrative) (Details) mMDth in Millions, $ in Millions	Mar. 31, 2024 USD ($) mMDth	Dec. 31, 2023 USD ($) mMDth
Derivative [Line Items]
Limit of GCA Volumes	20%
Derivative Asset, Subject to Master Netting Arrangement, after Offset \| $	$ 9.7	$ 13.9
Customer annual demand	20%
Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount \| mMDth	86	76.1

Risk Management Activities (Sch

Risk Management Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Risk Management Assets Current
Derivatives, Fair Value [Line Items]
Risk management assets	$ 3	$ 1.1
Risk Management Assets Noncurrent
Derivatives, Fair Value [Line Items]
Risk management assets	20.2	22.2
Risk Management Liabilities Current
Derivatives, Fair Value [Line Items]
Risk management liabilities	11.6	7.5
Risk Management Liabilities Noncurrent
Derivatives, Fair Value [Line Items]
Risk management liabilities	1.9	1.9
Commodity Price Risk Programs \| Risk Management Assets Current
Derivatives, Fair Value [Line Items]
Risk management assets	3	1.1
Commodity Price Risk Programs \| Risk Management Assets Noncurrent
Derivatives, Fair Value [Line Items]
Risk management assets	20.2	22.2
Commodity Price Risk Programs \| Risk Management Liabilities Current
Derivatives, Fair Value [Line Items]
Risk management liabilities	11.6	7.5
Commodity Price Risk Programs \| Risk Management Liabilities Noncurrent
Derivatives, Fair Value [Line Items]
Risk management liabilities	$ 1.9	$ 1.9

Risk Management Activities (S_2

Risk Management Activities (Schedule of Gains (Losses) on Commodity Price Risk Programs) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Deferred Derivative Gain (Loss)
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Liabilities	$ 23.3	$ 23.3
Deferred Derivative Gain (Loss)
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Assets	$ 20.1	$ 24.4

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Fair Value (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosure [Line Items]
Transfers between Fair Value Hierarchies	$ 0	$ 0
Allowance for Credit Loss	0.4	0.6
U.S. Treasury debt securities
Fair Value Disclosure [Line Items]
Allowance for Credit Loss	0	0
Corporate/Other debt securities
Fair Value Disclosure [Line Items]
Allowance for Credit Loss	$ 0.4	$ 0.6

Fair Value (Fair Value Of Finan

Fair Value (Fair Value Of Financial Assets And Liabilities Measured On A Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets
Available-for-sale, securities	$ 150.1	$ 159.1
Total	173.3	182.4
Liabilities
Total	13.5	9.4
Fair Value, Inputs, Level 1
Assets
Risk management assets	0	0
Available-for-sale, securities	0	0
Total	0	0
Liabilities
Risk management liabilities	0	0
Total	0	0
Significant Other Observable Inputs (Level 2)
Assets
Risk management assets	23.2	23.3
Available-for-sale, securities	150.1	159.1
Total	173.3	182.4
Liabilities
Risk management liabilities	13.5	9.4
Total	13.5	9.4
Significant Unobservable Inputs (Level 3)
Assets
Risk management assets	0	0
Available-for-sale, securities	0	0
Total	0	0
Liabilities
Risk management liabilities	0	0
Total	0	0
Available-for-sale Securities
Assets
Available-for-sale, securities	150.1	159.1
Risk management assets
Assets
Risk management assets	23.2	23.3
Liabilities
Risk management liabilities	$ 13.5	$ 9.4

Fair Value (Available-For-Sale

Fair Value (Available-For-Sale Securities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosure [Line Items]
Amortized Cost	$ 160.2	$ 169
Gross Unrealized Gains	0.6	0.8
Gross Unrealized Losses	(10.3)	(10.1)
Allowance for Credit Loss	(0.4)	(0.6)
Fair Value	150.1	159.1
Debt Securities, Available-for-Sale, Realized Gain	0.4
U.S. Treasury debt securities
Fair Value Disclosure [Line Items]
Amortized Cost	62.1	63.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3.3)	(3.2)
Allowance for Credit Loss	0	0
Fair Value	58.8	60.6
Debt Securities, Available-for-sale, Unrealized Loss Position	58.8	58.7
Corporate/Other debt securities
Fair Value Disclosure [Line Items]
Amortized Cost	98.1	105.2
Gross Unrealized Gains	0.6	0.8
Gross Unrealized Losses	(7)	(6.9)
Allowance for Credit Loss	(0.4)	(0.6)
Fair Value	91.3	98.5
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 72.7	$ 74.8

Fair Value (Carrying Amount And

Fair Value (Carrying Amount And Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Long-term Debt (including current portion), Carrying Amount	$ 11,748.6	$ 11,079.3
Long-term debt (including current portion), Estimated Fair Value	$ 10,852.3	$ 10,370.9

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details)	3 Months Ended
Income Taxes (Narrative) (Details)	Mar. 31, 2024 Rate	Mar. 31, 2023 Rate
Income Tax Disclosure [Abstract]
Effective income tax rates	16%	20.30%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	21%
Increase (Decrease) in Effective Tax Rate	(4.30%)

Pension And Other Postretirem_3

Pension And Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 0.7	$ 1.2
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 5.4	$ 5.6

Pension And Other Postretirem_4

Pension And Other Postretirement Benefits (Components Of The Plans' Net Periodic Benefits Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 5.4	$ 5.1
Interest cost	16.3	17.1
Expected return on assets	(23.8)	(23.6)
Amortization of prior service credit	0	0
Recognized actuarial loss	7.2	8.4
Total Net Periodic Benefits Cost	5.1	7
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	1.3	1.3
Interest cost	5.4	5.4
Expected return on assets	(4)	(3.8)
Amortization of prior service credit	(0.4)	(0.5)
Recognized actuarial loss	0.8	0.8
Total Net Periodic Benefits Cost	$ 3.1	$ 3.2

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) $ in Thousands		3 Months Ended		12 Months Ended
	Mar. 18, 2024 USD ($)	Mar. 31, 2024 USD ($) Rate MW	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Variable Interest Entity [Line Items]
Wind Power Purchase Agreement, Purchase Percentage \| Rate		100%
Payments to Acquire Assets, Investing Activities	$ 110,600
Business Acquisition, Transaction Costs				$ 54,700
Proceeds from Contributed Capital				2,160,000
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount				1,360,000
Income Taxes		$ 76,000	$ 85,800	$ 63,500
Rosewater
Variable Interest Entity [Line Items]
Nameplate Capacity \| MW		102
Indiana Crossroads Wind
Variable Interest Entity [Line Items]
Nameplate Capacity \| MW		302
Indiana Crossroads Solar
Variable Interest Entity [Line Items]
Nameplate Capacity \| MW		465
Dunns Bridge I
Variable Interest Entity [Line Items]
Nameplate Capacity \| MW		465

Variable Interest Entities (Sch

Variable Interest Entities (Schedule of VIE Assets and Liabilities) (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Public Utilities, Property, Plant and Equipment, Net	[1]	$ 22,946.1	$ 22,274.9
Current assets	[1]	2,060.2	4,499.4
Other Assets, Noncurrent		4,089.5	4,055.8
Total Assets		29,338.1	31,077.2
Current liabilities	[2]	3,125	5,265.1
Asset retirement obligations		509.6	480.5
Other noncurrent liabilities		297.7	298.6
Consolidated Variable Interest Entities
Variable Interest Entity [Line Items]
Public Utilities, Property, Plant and Equipment, Net		1,358.2	1,369.8
Current assets		60.8	63.6
Total Assets		1,419	1,433.4
Current liabilities		60.9	68.3
Asset retirement obligations		56.3	55.7
Total Liabilities		$ 117.2	$ 124

[1] Includes $1,358.2 million and $1,369.8 million at March 31, 2024 and December 31, 2023, respectively, of net property, plant and equipment assets and $60.8 million and $63.6 million at March 31, 2024 and December 31, 2023, respectively, of current assets of consolidated VIEs that may be used only to settle obligations of the consolidated VIEs. Note 4, "Noncontrolling Interests," for additional information. Includes $60.9 million and $68.3 million at March 31, 2024 and December 31, 2023, respectively, of current liabilities and $56.3 million and $55.7 million at March 31, 2024 and December 31, 2023, respectively, of other liabilities of consolidated VIEs that creditors do not have recourse to our general credit. Refer to Note 4, "Noncontrolling Interests," for additional information.

Long-Term Debt (Narrative) (Det

Long-Term Debt (Narrative) (Details) $ in Millions	Mar. 14, 2024 USD ($)	Mar. 31, 2024 MW
Rosewater
Debt Instrument [Line Items]
Nameplate Capacity \| MW		102
Senior Notes \| NiSource
Debt Instrument [Line Items]
Senior Notes	$ 650
Debt, Weighted Average Interest Rate	5.35%
Proceeds from Debt, Net of Issuance Costs	$ 642.6

Short-Term Borrowings (Narrativ

Short-Term Borrowings (Narrative) (Details)	3 Months Ended
Short-Term Borrowings (Narrative) (Details)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Feb. 09, 2024 USD ($)	Feb. 08, 2024 USD ($)	Jan. 03, 2024 USD ($)	Dec. 31, 2023 USD ($)
Short-term Debt [Line Items]
Short-term debt due to asset securitization	$ 0					$ 337,600,000
Termination Loans					$ 1,000,000,000	$ 1,000,000,000
Debt Instrument, Interest Rate, Stated Percentage						6.41%
Short-term Debt	$ 1,222,300,000					$ 3,048,600,000
Second Term Credit Agreement					$ 650,000,000	$ 650,000,000
Second TCA Debt Interest Rate						6.50%
Accounts Receivable Program
Short-term Debt [Line Items]
Number of Agreements	3
Cash From Financing Activities Related To The Change In Short-Term Borrowings Due To The Securitization Transactions	$ 337,600,000	$ 65,400,000
Securitization Transaction Fees	500,000	$ 900,000
Short-term Debt	419,800,000
Revolving Credit Facility
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,850,000,000
Long-term Line of Credit	0					$ 0
Commercial Paper
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 1,850,000,000	$ 1,500,000,000
Commercial paper outstanding	$ 1,222,300,000					$ 1,061,000,000
Short-term Debt, Weighted Average Interest Rate, at Point in Time	5.58%					5.65%

Other Commitments And Conting_2

Other Commitments And Contingencies (Narrative) (Details) $ in Thousands	Mar. 18, 2024 USD ($)	Mar. 31, 2024 USD ($) Rate	Dec. 31, 2023 USD ($)
Other Commitments And Contingencies [Line Items]
Guaranty Liabilities		$ 672,300	$ 646,100
Recorded reserves to cover environmental remediation at various sites		$ 77,800	80,000
Wind Power Purchase Agreement, Purchase Percentage \| Rate		100%
Payments to Acquire Assets, Investing Activities	$ 110,600
MGP Sites
Other Commitments And Contingencies [Line Items]
Number of waste disposal sites identified by program		53
Liability for Estimated Remediation Costs		$ 72,800	$ 73,700
Reasonably possible remediation costs variance from reserve		15,100
Standby Letters of Credit
Other Commitments And Contingencies [Line Items]
Long-term Line of Credit		$ 9,900

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (33.6)	$ (37.1)
Other Comprehensive Income (Loss) before reclassifications	(0.9)	1.7
Amounts reclassified from accumulated other comprehensive income (loss)	0.7	0.7
Net current-period other comprehensive income (loss)	(0.2)	2.4
Ending Balance	(33.8)	(34.7)
Gains and Losses on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(7.3)	(11.2)
Other Comprehensive Income (Loss) before reclassifications	(0.6)	1.7
Amounts reclassified from accumulated other comprehensive income (loss)	0.3	0.3
Net current-period other comprehensive income (loss)	(0.3)	2
Ending Balance	(7.6)	(9.2)
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(12.8)	(12.6)
Other Comprehensive Income (Loss) before reclassifications	(0.2)	0
Amounts reclassified from accumulated other comprehensive income (loss)	0.1	0.1
Net current-period other comprehensive income (loss)	(0.1)	0.1
Ending Balance	(12.9)	(12.5)
Pension and OPEB Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(13.5)	(13.3)
Other Comprehensive Income (Loss) before reclassifications	(0.1)	0
Amounts reclassified from accumulated other comprehensive income (loss)	0.3	0.3
Net current-period other comprehensive income (loss)	0.2	0.3
Ending Balance	$ (13.3)	$ (13)

Other, Net (Details)

Other, Net (Details) - USD ($) $ in Millions	3 Months Ended
Other, Net (Details) - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023
Other, Net [Abstract]
Interest income	$ 2.5	$ 1.8
AFUDC equity	11.3	4.8
Pension and other postretirement non-service benefit (cost)	(2.2)	(3.5)
Miscellaneous	(2.4)	(1.6)
Other, net	$ 9.2	$ 1.5

Business Segment Information (S

Business Segment Information (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 1,706.3	$ 1,966
Consolidated Operating Income (Loss)	583.4	531
Total Assets	29,338.1		$ 31,077.2
Eliminations
Segment Reporting Information [Line Items]
Revenues	(143.4)	(120)
Corporate and Other
Segment Reporting Information [Line Items]
Revenues	140.1	116.9
Consolidated Operating Income (Loss)	5	2.2
Total Assets	1,327.3		3,450.1
Corporate and Other \| Unaffiliated
Segment Reporting Information [Line Items]
Revenues	0.2	0.2
Corporate and Other \| Intersegment
Segment Reporting Information [Line Items]
Revenues	139.9	116.7
Columbia Operations
Segment Reporting Information [Line Items]
Revenues	956.9	1,051.9
Consolidated Operating Income (Loss)	362	351.8
Total Assets	13,789.8		13,664.5
Columbia Operations \| Unaffiliated
Segment Reporting Information [Line Items]
Revenues	953.7	1,048.9
Columbia Operations \| Intersegment
Segment Reporting Information [Line Items]
Revenues	3.2	3
NIPSCO Operations
Segment Reporting Information [Line Items]
Revenues	752.7	917.2
NIPSCO Operations \| Unaffiliated
Segment Reporting Information [Line Items]
Revenues	752.4	916.9
Consolidated Operating Income (Loss)	216.4	177
Total Assets	14,221		$ 13,962.6
NIPSCO Operations \| Intersegment
Segment Reporting Information [Line Items]
Revenues	$ 0.3	$ 0.3

Uncategorized Items - nix-20240

Label	Element	Value
Minimum [Member]
Commodity Contract Length	nix_CommodityContractLength	1 year
Maximum [Member]
Commodity Contract Length	nix_CommodityContractLength	3 years