Summary of Significant Accounting Policies - Property, Plant, and Equipment (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Mississippi Power [Member]	Dec. 31, 2011 Mississippi Power [Member]	Dec. 31, 2012 Gulf Power [Member]	Dec. 31, 2011 Gulf Power [Member]	Dec. 31, 2012 Georgia Power [Member]	Dec. 31, 2011 Georgia Power [Member]	Dec. 31, 2012 Alabama Power [Member]	Dec. 31, 2011 Alabama Power [Member]	Oct. 20, 2011 Plant Daniel Units 3 and 4 [Member] Mississippi Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation	$ 33,444,000,000	$ 31,751,000,000	$ 1,363,269,000	$ 1,362,567,000	$ 2,598,773,000	$ 2,283,494,000	$ 14,567,000,000	$ 13,675,000,000	$ 11,110,000,000	$ 10,982,000,000
Transmission	8,747,000,000	8,240,000,000	563,037,000	497,202,000	429,341,000	368,542,000	4,581,000,000	4,355,000,000	3,137,000,000	2,998,000,000
Distribution	15,958,000,000	15,458,000,000	802,718,000	784,655,000	1,069,065,000	1,030,546,000	8,373,000,000	8,125,000,000	5,714,000,000	5,517,000,000
General	4,208,000,000	3,413,000,000	225,723,000	176,408,000	161,379,000	161,322,000	1,695,000,000	1,621,000,000	1,434,000,000	1,300,000,000
Plant acquisition adjustment	124,000,000	124,000,000	81,412,000	81,408,000	2,286,000	2,542,000	28,000,000	28,000,000	12,000,000	12,000,000	81,400,000
Utility plant in service	62,481,000,000	58,986,000,000
Information technology equipment and software	230,000,000	220,000,000
Communications equipment	430,000,000	428,000,000
Other	110,000,000	110,000,000
Other plant in service	770,000,000	758,000,000
Total plant in service	$ 63,251,000,000	$ 59,744,000,000	$ 3,036,159,000	$ 2,902,240,000	$ 4,260,844,000	$ 3,846,446,000	$ 29,244,000,000	$ 27,804,000,000	$ 21,407,000,000	$ 20,809,000,000