Fair Value Measurements - Financial Instruments, Carrying Amount Not Equal to Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Long-term debt:
Long-term debt, Carrying Amount	$ 27,216	$ 23,814
Long-term debt, Fair Value	27,913	25,816
Alabama Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	6,849	6,586
Long-term debt, Fair Value	7,192	7,321
Georgia Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	10,145	9,673
Long-term debt, Fair Value	10,480	10,552
Gulf Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	1,303	1,362
Long-term debt, Fair Value	1,339	1,477
Mississippi Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	2,537	2,320
Long-term debt, Fair Value	2,413	2,382
Southern Power [Member]
Long-term debt:
Long-term debt, Carrying Amount	3,122	1,610
Long-term debt, Fair Value	$ 3,117	$ 1,785