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	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Southern Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value, Gross Asset	$ 24	$ 4
Georgia Power [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value, Gross Asset	$ 15	$ 2