CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Net Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Net income									$ 4,744	$ 2,300	$ 926
Less: Net income attributable to noncontrolling interests									10	(58)	(44)
Net income attributable to Southern Power	$ 440	$ 1,316	$ 899	$ 2,084	$ 278	$ 1,164	$ (154)	$ 938
Southern Power
Noncontrolling Interest [Line Items]
Net income									329	246	1,117
Less: Net income attributable to noncontrolling interests									$ (10)	$ 59	44
Less: Net income attributable to redeemable noncontrolling interests											2
Net income attributable to Southern Power	$ 23	$ 86	$ 174	$ 56	$ (48)	$ 92	$ 22	$ 121			$ 1,071