Consolidated Entities and Equity Method Investments - Net Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Net income									$ 2,300	$ 926	$ 2,529
Less: Net income attributable to noncontrolling interests									(58)	(44)	(32)
Net income attributable to Southern Power	$ 278	$ 1,164	$ (154)	$ 938	$ 496	$ 1,069	$ (1,381)	$ 658
Southern Power
Noncontrolling Interest [Line Items]
Net income									246	1,117	374
Less: Net income attributable to noncontrolling interests									$ 59	44	32
Less: Net income attributable to redeemable noncontrolling interests										2	4
Net income attributable to Southern Power	$ (48)	$ 92	$ 22	$ 121	$ 795	$ 124	$ 82	$ 70		$ 1,071	$ 338