Fair Value Measurements - Fair Value, Nature and Risk of Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Foreign Equity [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	117,000,000
Unfunded Commitments	0
Redemption Frequency	Monthly
Redemption Notice Period	5 days
Corporate bonds - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	9,000,000	32,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Equity - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	55,000,000	48,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily/Monthly	Daily/Monthly
Redemption Notice Period	Daily/7 days	Daily/7 days
Other - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	10,000,000	25,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Trust-owned life insurance [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	96,000,000	87,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	15 days	15 days
Money market funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	384,000,000	1,024,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Money market funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Unfunded Commitments		0
Minimum [Member] | Corporate bonds - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	1 day	1 day
Maximum [Member] | Foreign Equity [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	5 days
Maximum [Member] | Corporate bonds - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	3 days	3 days
Maximum [Member] | Equity - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	7 days	7 days
Maximum [Member] | Trust-owned life insurance [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	15 days	15 days
Southern Power [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	26,000,000	14,200,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Mississippi Power [Member] | Money market funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	125,600,000	133,900,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Alabama Power [Member] | Equity - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	55,000,000	48,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily/Monthly	Daily/Monthly
Redemption Notice Period	Daily/7 days	Daily/7 days
Redemption Notice Period	7 days	7 days
Alabama Power [Member] | Trust-owned life insurance [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	96,000,000	87,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	15 days	15 days
Redemption Notice Period	15 days	15 days
Alabama Power [Member] | Money market funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value		209,000,000
Unfunded Commitments	0	0
Redemption Frequency		Daily
Redemption Notice Period		Not applicable
Georgia Power [Member] | Foreign Equity [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	117,000,000
Unfunded Commitments	0
Redemption Frequency	Monthly
Redemption Notice Period	5 days
Georgia Power [Member] | Equity - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	9,000,000	32,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Georgia Power [Member] | Other - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	10,000,000	25,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Georgia Power [Member] | Cash Equivalents [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	15,000,000	13,000,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable
Georgia Power [Member] | Minimum [Member] | Equity - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	1 day
Georgia Power [Member] | Maximum [Member] | Foreign Equity [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	5 days
Georgia Power [Member] | Maximum [Member] | Equity - commingled funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Redemption Notice Period	3 days
Gulf Power [Member] | Money market funds [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	15,231,000	13,949,000
Unfunded Commitments	0	0
Redemption Frequency	Daily	Daily
Redemption Notice Period	Not applicable	Not applicable