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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Southern Company [Member]
Derivative [Line Items]
Gain (Loss)	$ 15	$ (1)	$ 19	$ (4)
Georgia Power [Member]
Derivative [Line Items]
Gain (Loss)	$ 7	$ 0	$ 9	$ 0