Income Taxes - Changes in Unrecognized Tax Benefits (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 120,000	$ 296,000	$ 199,000
Tax positions from current periods	13,000	46,000	62,000
Tax positions increases from prior periods	7,000	1,000	62,000
Tax positions decrease from prior periods	(56,000)	(111,000)	(27,000)
Reductions due to settlements	(10,000)	(112,000)	0
Reductions due to expired statute of limitations	(4,000)	0	0
Balance at end of year	70,000	120,000	296,000
Southern Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	2,600	2,300	100
Tax positions from current periods	700	400	700
Tax positions increases from prior periods			1,500
Tax positions decrease from prior periods	200	100
Reductions due to settlements	(200)	0	0
Balance at end of year	2,900	2,600	2,300
Gulf Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	2,892	3,870	1,639
Tax positions from current periods	2,630	540	1,027
Tax positions increases from prior periods	(515)		1,204
Tax positions decrease from prior periods		1,518
Reductions due to settlements	(1,030)	0	0
Balance at end of year	5,007	2,892	3,870
Mississippi Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	4,964	4,288	3,026
Tax positions from current periods	1,186	1,486	868
Tax positions increases from prior periods			611
Tax positions decrease from prior periods	(26)	810
Reductions due to settlements	(369)	0	0
Reductions due to expired statute of limitations	0	0	(217)
Balance at end of year	5,755	4,964	4,288
Alabama Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	32,000	43,000	6,000
Tax positions from current periods	5,000	6,000	6,000
Tax positions increases from prior periods			31,000
Tax positions decrease from prior periods	(4,000)	17,000
Reductions due to settlements	(2,000)	0	0
Balance at end of year	31,000	32,000	43,000
Georgia Power [Member]
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	47,000	237,000	181,000
Tax positions from current periods	3,000	9,000	52,000
Tax positions increases from prior periods	3,000	0	27,000
Tax positions decrease from prior periods	(19,000)	(87,000)	(23,000)
Reductions due to settlements	(8,000)	(112,000)	0
Reductions due to expired statute of limitations	(3,000)	0	0
Balance at end of year	$ 23,000	$ 47,000	$ 237,000