Noncontrolling Interest - Net Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Net income	$ 926	$ 2,529	$ 2,435
Less: Net income attributable to noncontrolling interests	(44)	(32)	(12)
SOUTHERN POWER CO
Noncontrolling Interest [Line Items]
Net income	1,117	374	229
Less: Net income attributable to noncontrolling interests	(44)	(32)	(12)
Less: Net income attributable to redeemable noncontrolling interests	2	4	2
Net income attributable to the Company	1,071	338	215
Noncontrolling Interests | SOUTHERN POWER CO
Noncontrolling Interest [Line Items]
Less: Net income attributable to noncontrolling interests	$ 44	$ 32	$ 12