Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions |
Jun. 30, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Securities due within one year | ||
| Derivative [Line Items] | ||
| Carrying Amount of the Hedged Item | $ (499) | $ (498) |
| Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | 1 | 2 |
| Securities due within one year | GEORGIA POWER CO | ||
| Derivative [Line Items] | ||
| Carrying Amount of the Hedged Item | (499) | (498) |
| Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | 1 | 2 |
| Long-term debt | ||
| Derivative [Line Items] | ||
| Carrying Amount of the Hedged Item | (2,087) | (2,052) |
| Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item | $ 7 | $ 41 |