Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Securities due within one year
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (500)	$ (498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	0	2
Securities due within one year | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	(500)	(498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	0	2
Long-term debt
Derivative [Line Items]
Carrying Amount of the Hedged Item	(2,093)	(2,052)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ (2)	$ 41