Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Sep. 30, 2016 USD ($)
Southern Company [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	$ 43,668
Long-term debt, including securities due within one year, Fair Value	47,227
Alabama Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	7,091
Long-term debt, including securities due within one year, Fair Value	7,961
Georgia Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	10,398
Long-term debt, including securities due within one year, Fair Value	11,582
Gulf Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	1,184
Long-term debt, including securities due within one year, Fair Value	1,267
Mississippi Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	2,981
Long-term debt, including securities due within one year, Fair Value	2,967
Southern Power [Member]
Long-term debt:
Long-term debt, including securities due within one year, Carrying Amount	4,608
Long-term debt, including securities due within one year, Fair Value	$ 4,821