Income Taxes - Changes in Unrecognized Tax Benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 7,000,000	$ 70,000,000	$ 120,000,000
Tax positions from current periods	64,000,000	3,000,000	13,000,000
Tax positions increase from prior periods	102,000,000	0	7,000,000
Tax positions decrease from prior periods	(3,000,000)	(66,000,000)	(56,000,000)
Reductions due to settlements	0	0	(10,000,000)
Reductions due to expired statute of limitations	0	0	(4,000,000)
Unrecognized tax benefits at end of year	170,000,000	7,000,000	70,000,000
Alabama Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year		31,000,000	32,000,000
Tax positions from current periods		0	5,000,000
Tax positions decrease from prior periods		(31,000,000)	(4,000,000)
Reductions due to settlements		0	(2,000,000)
Unrecognized tax benefits at end of year		0	31,000,000
Georgia Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year		23,000,000	47,000,000
Tax positions from current periods		0	3,000,000
Tax positions increase from prior periods		0	3,000,000
Tax positions decrease from prior periods		(23,000,000)	(19,000,000)
Reductions due to settlements		0	(8,000,000)
Reductions due to expired statute of limitations		0	(3,000,000)
Unrecognized tax benefits at end of year		0	23,000,000
Gulf Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	45,000	5,007,000	2,892,000
Tax positions from current periods	46,000	45,000	2,630,000
Tax positions increase from prior periods			515,000
Tax positions decrease from prior periods	(45,000)	(5,007,000)
Reductions due to settlements	0	0	(1,030,000)
Unrecognized tax benefits at end of year	46,000	45,000	5,007,000
Mississippi Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	3,840,000	5,755,000	4,964,000
Tax positions from current periods	58,148,000	226,000	1,186,000
Tax positions increase from prior periods	102,833,000
Tax positions decrease from prior periods		(2,141,000)	(26,000)
Reductions due to settlements	0	0	(369,000)
Unrecognized tax benefits at end of year	164,821,000	3,840,000	5,755,000
Southern Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	1,500,000	2,900,000	2,600,000
Tax positions from current periods	4,700,000	1,600,000	700,000
Tax positions decrease from prior periods	(1,500,000)	(3,000,000)	(200,000)
Reductions due to settlements	0	0	(200,000)
Unrecognized tax benefits at end of year	$ 4,700,000	$ 1,500,000	$ 2,900,000