Commitments and Contingencies, Legal Contingencies (Details) (USD $)	3 Months Ended			13 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Pacific Northwest FERC Refund Proceeding [Member] Factor	Jun. 30, 2001 Pacific Northwest FERC Refund Proceeding [Member]
Legal Contingencies [Abstract]
Accrual for legal contingency			$ 0
Minimum amount of damages claimed by plaintiff			34,000,000
Sales to the City of Seattle	1,203,543,000	1,117,457,000		50,000,000
Estimated City of Seattle's claim for refunds not including interest			$ 28,000,000
Number of factors considered in assessment			2