DERIVATIVES - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Long-term debt - Fair Value Hedging - USD ($) $ in Millions |
Dec. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|
| 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 |