Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Long-term debt:
Long-term debt, Carrying Amount	$ 21,915
Long-term debt, Fair Value	23,644
Alabama Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	6,179
Long-term debt, Fair Value	6,853
Georgia Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	9,639
Long-term debt, Fair Value	10,316
Gulf Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,246
Long-term debt, Fair Value	1,353
Mississippi Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	2,211
Long-term debt, Fair Value	2,294
Southern Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,308
Long-term debt, Fair Value	$ 1,448