Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Southern Company [Member]
Long-term debt:
Long-term debt, Carrying Amount	$ 24,241
Long-term debt, Fair Value	26,350
Alabama Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	6,922
Long-term debt, Fair Value	7,696
Georgia Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	9,801
Long-term debt, Fair Value	10,733
Gulf Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,370
Long-term debt, Fair Value	1,501
Mississippi Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	2,251
Long-term debt, Fair Value	2,323
Southern Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,621
Long-term debt, Fair Value	$ 1,789