Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Mar. 31, 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	(2,065)	(2,052)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	28	41
Long-term debt | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	0	0
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 0	$ 0