Fair Value Measurements - Textual (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Maximum number of months related to maturities in the portfolio not to exceeded from the date of purchase	13 months
Maximum number of days related to dollar-weighted average portfolio maturities regarding commingled funds	90 days
Georgia Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Notices Of Withdrawal Foreign Equity Funds	20.00%
Maximum number of months related to maturities in the portfolio not to exceeded from the date of purchase	13 months
Maximum number of days related to dollar-weighted average portfolio maturities regarding commingled funds	90 days
Minimum [Member] | Georgia Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Withdrawal Of Foreign Equity Fund Investment	1
Foreign Equity Fund Investment	10