Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Long-term debt:
Long-term debt, Carrying Amount	$ 21,942
Long-term debt, Fair Value	22,734
Alabama Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	6,179
Long-term debt, Fair Value	6,573
Georgia Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	9,622
Long-term debt, Fair Value	9,878
Gulf Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,335
Long-term debt, Fair Value	1,391
Mississippi Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	2,209
Long-term debt, Fair Value	2,201
Southern Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,316
Long-term debt, Fair Value	$ 1,377