Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Securities due within one year
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	$ (498)	$ (746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	2	3
Securities due within one year \| Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	(498)	(746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	2	3
Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	(2,052)	(2,553)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	41	35
Long-term debt \| Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	0	(498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 0	$ 1