Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Mar. 31, 2016 USD ($)
Southern Company [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	$ 28,341
Long-term debt, including securities due within one year, Fair Value	29,827
Alabama Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	7,089
Long-term debt, including securities due within one year, Fair Value	7,688
Georgia Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	10,549
Long-term debt, including securities due within one year, Fair Value	11,400
Gulf Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	1,303
Long-term debt, including securities due within one year, Fair Value	1,366
Mississippi Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	3,209
Long-term debt, including securities due within one year, Fair Value	2,938
Southern Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	3,123
Long-term debt, including securities due within one year, Fair Value	$ 3,171