Derivatives - Pre-tax Effects of Derivatives Designated as Fair Value Hedging Instruments (Details) - Interest Rate Contract [Member] - Interest Expense [Member] - Fair Value Hedging [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Southern Company [Member]
Derivative [Line Items]
Gain (Loss)	$ 20	$ 7
Georgia Power [Member]
Derivative [Line Items]
Gain (Loss)	$ 14	$ 6