Effective Tax Rate and Unrecognized Tax Benefits - Narrative (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended												1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Alabama Power [Member]	Sep. 30, 2013 Alabama Power [Member]	Sep. 30, 2014 Georgia Power [Member]	Sep. 30, 2013 Georgia Power [Member]	Sep. 30, 2014 Gulf Power [Member]	Sep. 30, 2013 Gulf Power [Member]	Sep. 30, 2014 Mississippi Power [Member]	Sep. 30, 2013 Mississippi Power [Member]	Sep. 30, 2014 Southern Power [Member]	Sep. 30, 2013 Southern Power [Member]	Sep. 30, 2014 Kemper Igcc [Member]	Sep. 30, 2014 Kemper Igcc [Member] Mississippi Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	33.90%	33.90%	39.00%	39.30%	37.20%	38.00%	37.40%	37.60%	(45.50%)	(42.10%)	14.40%	20.50%
Unrecognized tax benefit													$ 100	$ 100
Unrecognized tax benefit, associated interest													$ 2	$ 2