Noncontrolling Interest (Details) - Southern Power [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Noncontrolling Interest [Roll Forward]
Redeemable Put Option, Beginning balance	$ 39	$ 29	$ 8
Net income attributable to redeemable noncontrolling interest	2	4	4
Distributions to redeemable noncontrolling interest	0	(1)	0
Capital contributions from redeemable noncontrolling interest	2	7	17
Redeemable Put Option, Ending balance	$ 43	$ 39	$ 29