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ASSET RETIREMENT OBLIGATIONS - Fair Value Increases (Decreases) of the Funds (Details) - Securities held in the Funds - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Fair value increases (decreases) |  |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |  |
Fair value increases (decreases) of the Funds | $ 281 | $ (360) | $ 274
Unrealized gains (losses) |  |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |  |
Fair value increases (decreases) of the Funds | 241 | (391) | (27)
Alabama Power | Fair value increases (decreases) |  |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |  |
Fair value increases (decreases) of the Funds | 157 | (171) | 200
Alabama Power | Unrealized gains (losses) |  |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |  |
Fair value increases (decreases) of the Funds | 119 | (204) | (30)
Georgia Power | Fair value increases (decreases) |  |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |  |
Fair value increases (decreases) of the Funds | 124 | (189) | 74
Georgia Power | Unrealized gains (losses) |  |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |  |
Fair value increases (decreases) of the Funds | $ 122 | $ (187) | $ 3

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