Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Securities due within one year
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (497)	$ (746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	3	3
Securities due within one year | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	(497)	(746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	3	3
Long-term Debt
Derivative [Line Items]
Carrying Amount of the Hedged Item	(2,528)	(2,553)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	63	35
Long-term Debt | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	(497)	(498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 3	$ 1