Effective Tax Rate and Unrecognized Tax Benefits - Changes for Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	$ 70
Tax positions from current periods	3
Balance as of March 31, 2013	73
Alabama Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	31
Tax positions from current periods	1
Balance as of March 31, 2013	32
Georgia Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	23
Tax positions from current periods	1
Balance as of March 31, 2013	24
Gulf Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	5
Tax positions from current periods	0
Balance as of March 31, 2013	5
Mississippi Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	6
Tax positions from current periods	0
Balance as of March 31, 2013	6
Southern Power [Member]
Changes for Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of December 31, 2012	3
Tax positions from current periods	0
Balance as of March 31, 2013	$ 3