Fair Value Measurements (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012
Fair Value Measurements (Textual) [Abstract]
Increase in fair value of funds including reinvested interest and dividends	$ 53	$ 116
Fair Value Measurement (Textual) [Abstract]
Maximum number of months related to maturities in the portfolio not to exceeded from date of purchase		13 months
Maximum number of days related to dollar-weighted average portfolio maturities regarding commingled funds		90 days
Maximum maturity for longer term investment grade fixed income obligations (in years)		5 years
Minimum number of months related to the reset date of maturities in the portfolio with put features or floating rates		13 months
Alabama Power [Member]
Fair Value Measurements (Textual) [Abstract]
Increase in fair value of funds including reinvested interest and dividends	27	60
Georgia Power [Member]
Fair Value Measurements (Textual) [Abstract]
Nuclear decommissioning trusts	54	54
Increase in fair value of funds including reinvested interest and dividends	$ 26	$ 56