Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014 MW
Lancaster Power Purchase Agreement [Member]
Evaluated Power Capacity	270.0
Future contractual obligation	$ 286
Palouse Wind Power Purchase Agreement [Member]
Evaluated Power Capacity	105.0
Expected power production, in megawatts	40
Future contractual obligation	$ 595
Minimum [Member] | Lancaster Power Purchase Agreement [Member]
Minimum estimated life of plant, in years	15 years
Maximum [Member] | Lancaster Power Purchase Agreement [Member]
Minimum estimated life of plant, in years	25 years