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SEGMENT AND RELATED INFORMATION - Gas Revenues (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2023 | Jun. 30, 2023 | Dec. 31, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | $ 26,724 | $ 25,253 | $ 29,279
Other segment items |  |  |  | 13,995 | 13,954 | 19,426
Depreciation and amortization |  |  |  | 4,755 | 4,525 | 3,663
Earnings from equity method investments |  |  |  | 139 | 144 | 151
Interest expense |  |  |  | 2,743 | 2,446 | 2,022
Income taxes (benefit) |  |  |  | 969 | 496 | 795
Segment net income (loss) |  |  |  | 4,401 | 3,976 | 3,524
Total assets | $ 139,331 |  | $ 134,891 | 145,180 | 139,331 | 134,891
Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 4,456 | 4,702 | 5,962
Other segment items |  |  |  | 2,613 | 3,124 | 4,536
Depreciation and amortization |  |  |  | 650 | 582 | 559
Earnings from equity method investments |  |  |  | 146 | 140 | 148
Interest expense |  |  |  | 341 | 310 | 263
Income taxes (benefit) |  |  |  | 258 | 211 | 180
Segment net income (loss) |  |  |  | 740 | 615 | 572
Total assets | 25,083 |  | 24,621 | 26,177 | 25,083 | 24,621
Estimated loss on regulatory disallowance |  |  |  | 0 | (96) | 0
Southern Company Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Natural Gas Storage Facilities |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Gain on dispositions, net |  |  | (131) |  |  |
Gain (loss) on dispositions, after tax |  |  | (99) |  |  |
Nicor Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Estimated loss on regulatory disallowance | (58) | $ (38) |  | 96 |  |
Estimated loss on regulatory disallowance, after tax | (44) | $ (28) |  | 72 |  |
Operating Segments |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 26,059 | 24,700 | 28,835
Other segment items |  |  |  | 13,342 | 13,405 | 18,793
Depreciation and amortization |  |  |  | 4,684 | 4,447 | 3,588
Earnings from equity method investments |  |  |  | 154 | 139 | 148
Interest expense |  |  |  | 1,713 | 1,584 | 1,330
Income taxes (benefit) |  |  |  | 1,261 | 794 | 1,028
Segment net income (loss) |  |  |  | 5,213 | 4,609 | 4,244
Total assets | 137,728 |  | 132,904 | 143,382 | 137,728 | 132,904
Operating Segments | Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 4,447 | 4,685 | 5,937
Other segment items |  |  |  | 2,598 | 3,109 | 4,401
Depreciation and amortization |  |  |  | 649 | 581 | 537
Earnings from equity method investments |  |  |  | 146 | 140 | 148
Interest expense |  |  |  | 349 | 310 | 259
Income taxes (benefit) |  |  |  | 244 | 195 | 217
Segment net income (loss) |  |  |  | 753 | 630 | 671
Total assets | 26,055 |  | 25,233 | 27,336 | 26,055 | 25,233
All Other |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 843 | 718 | 593
Other segment items |  |  |  | 802 | 699 | 771
Depreciation and amortization |  |  |  | 71 | 78 | 75
Earnings from equity method investments |  |  |  | (17) | 5 | 3
Interest expense |  |  |  | 1,030 | 879 | 694
Income taxes (benefit) |  |  |  | (292) | (298) | (233)
Segment net income (loss) |  |  |  | (785) | (635) | (711)
Total assets | 2,446 |  | 2,665 | 2,371 | 2,446 | 2,665
All Other | Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 23 | 36 | 55
Other segment items |  |  |  | 29 | 34 | 165
Depreciation and amortization |  |  |  | 1 | 1 | 22
Earnings from equity method investments |  |  |  | 0 | 0 | 0
Interest expense |  |  |  | (8) | 0 | 4
Income taxes (benefit) |  |  |  | 14 | 16 | (37)
Segment net income (loss) |  |  |  | (13) | (15) | (99)
Total assets | 9,675 |  | 8,943 | 10,047 | 9,675 | 8,943
Eliminations |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | (178) | (165) | (149)
Other segment items |  |  |  | (149) | (150) | (138)
Depreciation and amortization |  |  |  | 0 | 0 | 0
Earnings from equity method investments |  |  |  | 2 | 0 | 0
Interest expense |  |  |  | 0 | (17) | (2)
Income taxes (benefit) |  |  |  | 0 | 0 | 0
Segment net income (loss) |  |  |  | (27) | 2 | (9)
Total assets | (843) |  | (678) | (573) | (843) | (678)
Eliminations | Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | (14) | (19) | (30)
Other segment items |  |  |  | (14) | (19) | (30)
Depreciation and amortization |  |  |  | 0 | 0 | 0
Earnings from equity method investments |  |  |  | 0 | 0 | 0
Interest expense |  |  |  | 0 | 0 | 0
Income taxes (benefit) |  |  |  | 0 | 0 | 0
Segment net income (loss) |  |  |  | 0 | 0 | 0
Total assets | (10,647) |  | (9,555) | (11,206) | (10,647) | (9,555)
Gas distribution operations | Operating Segments | Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 3,899 | 4,105 | 5,267
Other segment items |  |  |  | 2,236 | 2,702 | 3,907
Depreciation and amortization |  |  |  | 630 | 561 | 516
Earnings from equity method investments |  |  |  | 0 | 0 | 0
Interest expense |  |  |  | 311 | 275 | 229
Income taxes (benefit) |  |  |  | 172 | 126 | 145
Segment net income (loss) |  |  |  | 550 | 441 | 470
Total assets | 22,906 |  | 22,040 | 24,067 | 22,906 | 22,040
Gas Pipeline Investments | Operating Segments | Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 32 | 32 | 32
Other segment items |  |  |  | 6 | 5 | 6
Depreciation and amortization |  |  |  | 5 | 5 | 5
Earnings from equity method investments |  |  |  | 146 | 140 | 148
Interest expense |  |  |  | 35 | 32 | 27
Income taxes (benefit) |  |  |  | 31 | 32 | 35
Segment net income (loss) |  |  |  | 101 | 98 | 107
Total assets | 1,534 |  | 1,577 | 1,573 | 1,534 | 1,577
Gas marketing services | Operating Segments | Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 516 | 548 | 638
Other segment items |  |  |  | 356 | 402 | 488
Depreciation and amortization |  |  |  | 14 | 15 | 16
Earnings from equity method investments |  |  |  | 0 | 0 | 0
Interest expense |  |  |  | 3 | 3 | 3
Income taxes (benefit) |  |  |  | 41 | 37 | 37
Segment net income (loss) |  |  |  | 102 | 91 | 94
Total assets | 1,615 |  | 1,616 | 1,696 | 1,615 | 1,616
Southern Company Gas |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 4,456 | 4,702 | 5,962
Southern Company Gas | Gas distribution operations |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 3,899 | 4,090 | 5,240
Southern Company Gas | Gas marketing services |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 516 | 548 | 638
Southern Company Gas | Other Gas Revenue |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 41 | 64 | 84
Southern Company Gas | Operating Segments |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating revenues |  |  |  | 4,456 | 4,702 | 5,962
Other segment items |  |  |  | 2,613 | 3,124 | 4,536
Depreciation and amortization |  |  |  | 650 | 582 | 559
Earnings from equity method investments |  |  |  | 146 | 140 | 148
Interest expense |  |  |  | 341 | 310 | 263
Income taxes (benefit) |  |  |  | 258 | 211 | 180
Segment net income (loss) |  |  |  | 740 | 615 | 572
Total assets | $ 25,083 |  | $ 24,621 | $ 26,177 | $ 25,083 | $ 24,621

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