Noncontrolling Interest (Details) (Southern Power [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Southern Power [Member]
Noncontrolling Interest [Roll Forward]
Redeemable Put Option, Beginning balance	$ 28,778,000	$ 8,100,000	$ 3,800,000
Net income attributable to redeemable noncontrolling interest	4,000,000	3,900,000	900,000
Distributions to redeemable noncontrolling interest	(1,100,000)	(500,000)	0
Capital contributions from redeemable noncontrolling interest	7,500,000	17,300,000	3,400,000
Redeemable Put Option, Ending balance	$ 39,241,000	$ 28,778,000	$ 8,100,000