Effective Tax Rate and Unrecognized Tax Benefits - Changes for Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Mar. 31, 2013	Sep. 30, 2013
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	$ 70	$ 70
Tax positions from current periods		3
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(66)
Balance as of September 30, 2013		7
Alabama Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	31	31
Tax positions from current periods		0
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(31)
Balance as of September 30, 2013		0
Georgia Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	23	23
Tax positions from current periods		0
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(23)
Balance as of September 30, 2013		0
Gulf Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	5	5
Tax positions from current periods		0
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(5)
Balance as of September 30, 2013		0
Mississippi Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	6	6
Tax positions from current periods		0
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(2)
Balance as of September 30, 2013		4
Southern Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	3	3
Tax positions from current periods		2
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(3)
Balance as of September 30, 2013		$ 2