Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Southern Company [Member]
Long-term debt:
Long-term debt, Carrying Amount	$ 23,936
Long-term debt, Fair Value	25,318
Alabama Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	6,625
Long-term debt, Fair Value	7,195
Georgia Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	9,597
Long-term debt, Fair Value	10,167
Gulf Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,444
Long-term debt, Fair Value	1,517
Mississippi Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	2,365
Long-term debt, Fair Value	2,397
Southern Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,629
Long-term debt, Fair Value	$ 1,745