Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Long-term debt:
Long-term debt, Carrying Amount	$ 22,896
Long-term debt, Fair Value	23,963
Alabama Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	6,228
Long-term debt, Fair Value	6,689
Georgia Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	9,593
Long-term debt, Fair Value	9,997
Gulf Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,233
Long-term debt, Fair Value	1,308
Mississippi Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	2,346
Long-term debt, Fair Value	2,346
Southern Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,620
Long-term debt, Fair Value	$ 1,709