Income Taxes - Impact of Unrecognized Tax Benefits on Effective Tax Rate, If Recognized (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Impact on effective tax rate
Tax positions impacting the effective tax rate	$ 10,000	$ 7,000	$ 5,000
Tax positions not impacting the effective tax rate	160,000	0	65,000
Balance of unrecognized tax benefits	170,000	7,000	70,000	120,000
Alabama Power [Member]
Impact on effective tax rate
Balance of unrecognized tax benefits		0	31,000	32,000
Georgia Power [Member]
Impact on effective tax rate
Balance of unrecognized tax benefits		0	23,000	47,000
Gulf Power [Member]
Impact on effective tax rate
Tax positions impacting the effective tax rate	46	45	45
Tax positions not impacting the effective tax rate	0	0	4,962
Balance of unrecognized tax benefits	46	45	5,007	2,892
Mississippi Power [Member]
Impact on effective tax rate
Tax positions impacting the effective tax rate	4,341	3,840	3,656
Tax positions not impacting the effective tax rate	160,480	0	2,099
Balance of unrecognized tax benefits	164,821	3,840	5,755	4,964
Southern Power [Member]
Impact on effective tax rate
Tax positions impacting the effective tax rate	4,700	1,500	300
Tax positions not impacting the effective tax rate	0	0	2,600
Balance of unrecognized tax benefits	$ 4,700	$ 1,500	$ 2,900	$ 2,600