Derivatives - Pre-tax Effects of Derivatives as Fair Value Hedging Relationships (Details) - Interest Rate Contract [Member] - Interest Expense [Member] - Fair Value Hedging [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Southern Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets, fair value, gross asset	$ (8)	$ 20
Georgia Power [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets, fair value, gross asset	$ (1)	$ 14