Commitments and Contingencies, Variable Interest Entities (Details) - MW	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Purchased Power Agreements (PPAs) [Abstract]
VIE Purchase Power Agreement Expiration Date	2032
Independent Power Producing Entities
Purchased Power Agreements (PPAs) [Abstract]
Generating capacity (in MW)	1,571	1,802