Income Taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 170	$ 7	$ 70
Tax positions from current periods	43	64	3
Tax positions increase from prior periods	240	102	0
Tax positions decrease from prior periods	(20)	(3)	(66)
Unrecognized tax benefits at end of year	433	170	7
Georgia Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	0	0	23
Tax positions increase from prior periods	3	0	0
Tax positions decrease from prior periods	0	0	(23)
Unrecognized tax benefits at end of year	3	0	0
Mississippi Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	165	4	6
Tax positions from current periods	32	58	0
Tax positions increase from prior periods	224	103
Tax positions decrease from prior periods			(2)
Unrecognized tax benefits at end of year	421	165	4
Southern Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	5	2	3
Tax positions from current periods	9	5	2
Tax positions decrease from prior periods	(6)	(2)	(3)
Unrecognized tax benefits at end of year	$ 8	$ 5	$ 2