Derivatives - Schedule of Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - Long-term debt - USD ($) $ in Millions |
Sep. 30, 2023 |
Dec. 31, 2022 |
|---|---|---|
| Derivative [Line Items] | ||
| Carrying Amount of the Hedged Item | $ (2,873) | $ (2,927) |
| Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | 328 | 282 |
| SOUTHERN Co GAS | ||
| Derivative [Line Items] | ||
| Carrying Amount of the Hedged Item | (402) | (415) |
| Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | $ 95 | $ 81 |