Derivatives - Pre-tax Effects of Derivatives as Fair Value Hedging Relationships (Details) - Interest Rate Contract - Interest expense, net of amounts capitalized - Fair Value Hedging [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Southern Company
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets, fair value, gross asset	$ 7	$ 4	$ (1)	$ 24
GEORGIA POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets, fair value, gross asset	$ 0	$ 0	$ (1)	$ 15