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CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - SEGCO Equity Method Investments Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2021 USD ($) MW | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Alabama Power |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Ownership percentage, equity method investment | 50.00% |  |
Percent ownership | 14.00% |  |
Alabama Power | SEGCO |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Total megawatt capacity (in MWs) | MW | 1,020 |  |
Share of purchased power | $ 75 | $ 67 | $ 93
Dividends paid by equity method investment | $ 14 | 12 | 14
Georgia Power |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Ownership percentage, equity method investment | 50.00% |  |
Georgia Power | SEGCO |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Share of purchased power | $ 77 | $ 69 | $ 95
SEGCO | Alabama Power |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Percent ownership | 86.00% |  |

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