Commitments and Contingencies, Variable Interest Entities (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013 MW
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member]
Purchased Power Agreements [Abstract]
Generating capacity (in MW)	827	827
Minimum
Purchased Power Agreements [Abstract]
Coal Supply Agreement Expiration	2016
Maximum
Purchased Power Agreements [Abstract]
Purchase Power Agreement Duration VIE, Maximum	2033
Coal Supply Agreement Expiration	2017