Fair Value Measurements - Narrative (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds including reinvested interest and dividends	$ (65)	$ (33)
Georgia Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Notices Of Withdrawal Foreign Equity Funds	20.00%	20.00%
Increase (decrease) in fair value of funds including reinvested interest and dividends	$ (26)	$ (14)
Georgia Power [Member] | Other - commingled funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Maximum Number of Days Related to Dollar Weighted Average Portfolio Maturities Regarding Commingled Funds		90 days
Georgia Power [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Withdrawal Of Foreign Equity Fund Investment	1	$ 1
Foreign Equity Fund Investment	10	10
Alabama Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds including reinvested interest and dividends	$ (39)	$ (19)