Noncontrolling Interest - Redeemable Noncontrolling Interest (Details) - Southern Power [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Noncontrolling Interest [Roll Forward]
Redeemable Put Option, Beginning balance	$ 43	$ 39	$ 29
Net income attributable to redeemable noncontrolling interest	4	2	4
Distributions to redeemable noncontrolling interest	(1)	0	(1)
Capital contributions from redeemable noncontrolling interest	118	2	7
Redeemable Put Option, Ending balance	$ 164	$ 43	$ 39