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DERIVATIVES - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Long-term debt - Fair Value Hedging - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
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Derivative Instruments, Gain (Loss) [Line Items] |  |
Carrying Amount of the Hedged Item | $ (2,936) | $ (3,024)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | 242 | 235
Southern Company Gas |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Carrying Amount of the Hedged Item | (422) | (427)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | $ 75 | $ 70

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