Commitments and Contingencies, Purchased Power Agreements (Details) (Independent Power Producing Entities)	3 Months Ended
	Sep. 30, 2014 MW	Dec. 31, 2013 MW
Independent Power Producing Entities
Purchased Power Agreements [Abstract]
Generating capacity (in MW)	1,802	1,441
Purchase Power Agreement Duration, Maximum (year)	2032