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SEGMENT AND RELATED INFORMATION - Narrative (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 USD ($) segment state | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2014
Segment Reporting Information [Line Items] |  |  |  |
Total operating revenues | $ 23,463 | $ 21,097 | $ 22,596 |
Southern Power |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total operating revenues | 1,605 | 1,119 | 1,220 |
Southern Company Gas |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total operating revenues | $ 6,293 | 5,039 | 5,598 |
Number of reportable segments | segment | 3 |  |  |
Number of states in which entity operates | state | 4 |  |  |
Southern Natural Gas Company, LLC | Southern Company Gas |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Ownership percentage, equity method investment | 50.00% |  |  |
Dalton Pipeline | Southern Company Gas |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Ownership percentage, equity method investment | 50.00% |  |  |
PennEast Pipeline | Southern Company Gas |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Ownership percentage, equity method investment | 20.00% |  |  | 20.00%
Atlantic Coast Pipeline | Southern Company Gas |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Ownership percentage, equity method investment | 5.00% |  |  |
Wholesale revenues, affiliates | Southern Power | Traditional Electric Operating Companies |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total operating revenues | $ 515 | 364 | 398 |
Natural gas | Southern Company Gas | Traditional Electric Operating Companies |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total operating revenues |  |  | 14 |
Natural gas | Southern Company Gas | Southern Power |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total operating revenues | $ 18 | $ 26 | $ 64 |

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