| Cover Page Document | Nov. 16, 2023 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 16, 2023 |
| Entity File Number | 1-14174 |
| Entity Registrant Name | Southern Company Gas |
| Entity Tax Identification Number | 58-2210952 |
| Entity Incorporation, State or Country Code | GA |
| Entity Address, Address Line One | Ten Peachtree Place, NE |
| Entity Address, City or Town | Atlanta |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 30309 |
| City Area Code | 404 |
| Local Phone Number | 584-4000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001004155 |
| Amendment Flag | false |
