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DERIVATIVES - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Long-term debt - Fair Value Hedging - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
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Derivative Instruments, Gain (Loss) [Line Items] |  |
Carrying Amount of the Hedged Item | $ (3,024) | $ (2,927)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | 235 | 282
Southern Company Gas |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Carrying Amount of the Hedged Item | (427) | (415)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | $ 70 | $ 81

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