Fair Value Measurements - Fair Value Measurements Calculated at Net Asset Value Per Share (Details) (USD $)	3 Months Ended
	Mar. 31, 2013
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	$ 120,000,000
Unfunded Commitments	0
Redemption Frequency	Monthly
Redemption Notice Period, Description	5 days
Foreign Equity [Member] | Georgia 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	120,000,000
Unfunded Commitments	0
Redemption Frequency	Monthly
Redemption Notice Period, Description	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	7,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	1 to 3 days
Corporate bonds - commingled funds [Member] | Georgia 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	7,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	Not applicable
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	74,000,000
Unfunded Commitments	0
Redemption Frequency	Daily/Monthly
Redemption Notice Period, Description	Daily/7 days
Other - commingled funds [Member] | Alabama 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	56,000,000
Unfunded Commitments	0
Redemption Frequency	Daily/Monthly
Redemption Notice Period, Description	Daily/7 days
Other - commingled funds [Member] | Georgia 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	18,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	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	100,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	15 days
Trust owned life insurance [Member] | Alabama 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	100,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	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	223,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	Not applicable
Money market funds [Member] | Georgia 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	27,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	Not applicable
Money market funds [Member] | Gulf 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	16,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	Not applicable
Money market funds [Member] | Mississippi 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	122,000,000
Unfunded Commitments	0
Redemption Frequency	Daily
Redemption Notice Period, Description	Not applicable
Money market funds [Member] | 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	27,000,000
Unfunded Commitments	$ 0
Redemption Frequency	Daily
Redemption Notice Period, Description	Not applicable
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
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] | Foreign Equity [Member] | Georgia Power [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
Maximum [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
Redemption Notice Period	7 days
Maximum [Member] | Other - commingled funds [Member] | Alabama Power [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
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
Maximum [Member] | Trust owned life insurance [Member] | Alabama Power [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