Summary of Significant Accounting Policies - Asset Retirement Obligations (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 1,344,000	$ 1,266,000
Liabilities incurred	45,000	1,000
Liabilities settled	(16,000)	(13,000)
Accretion	(112,000)	(82,000)
Cash flow revisions	272,000	8,000
Balance at end of year	1,757,000	1,344,000
Mississippi Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	19,148	18,601
Liabilities incurred	20,989	137
Liabilities settled	(282)	(644)
Accretion	1,874	1,054
Cash flow revisions	386	0
Balance at end of year	42,115	19,148
Gulf Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	10,729	11,470
Liabilities incurred	0	106
Liabilities settled	(107)	(1,050)
Accretion	507	545
Cash flow revisions	4,926	(342)
Balance at end of year	16,055	10,729
Georgia Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	757,000	712,000
Liabilities incurred	24,000	0
Liabilities settled	(15,000)	(9,000)
Accretion	72,000	45,000
Cash flow revisions	267,000	9,000
Balance at end of year	1,105,000	757,000
Alabama Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	553,000	520,000
Liabilities incurred	0	0
Liabilities settled	(1,000)	(2,000)
Accretion	37,000	35,000
Balance at end of year	$ 589,000	$ 553,000