Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in fair value, tax	$ 16	$ (5)
Reclassification adjustment for cash flow hedge, gain (loss), tax	(6)	(1)
Reclassification adjustment for pension and other post retirement benefit plans, tax	0	0
ALABAMA POWER CO
Changes in fair value, tax	0	0
Reclassification adjustment for cash flow hedge, gain (loss), tax	1	1
GULF POWER CO
Changes in fair value, tax	0	0
MISSISSIPPI POWER CO
Changes in fair value, tax	(1)	0
SOUTHERN POWER CO
Changes in fair value, tax	16	(4)
Reclassification adjustment for cash flow hedge, gain (loss), tax	(8)	(3)
SOUTHERN Co GAS
Changes in fair value, tax	0	(1)
Reclassification adjustment for cash flow hedge, gain (loss), tax	1	0
Reclassification adjustment for pension and other post retirement benefit plans, tax	$ 0	$ (1)