Fair Value Measurements - Financial Instruments, Carrying Amount Not Equal to Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Long-term debt:
Long-term debt, Carrying Amount	$ 21,530,000	$ 20,272,000
Long-term debt, Fair Value	23,480,000	22,144,000
Mississippi Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,840,933	1,343,596
Long-term debt, Fair Value	1,956,799	1,426,808
Southern Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,306,000	1,303,000
Long-term debt, Fair Value	1,444,000	1,397,000
Georgia Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	9,624,000	8,418,000
Long-term debt, Fair Value	10,427,000	9,209,000
Alabama Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	6,179,000	6,132,000
Long-term debt, Fair Value	6,899,000	6,874,000
Gulf Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,245,870	1,235,447
Long-term debt, Fair Value	$ 1,367,404	$ 1,350,237