Commitments and Contingencies, Legal Contingencies (Details) (USD $)	3 Months Ended								12 Months Ended				13 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 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	1,074,442,000	1,044,300,000	966,429,000	1,117,457,000	1,031,453,000	992,287,000	869,501,000	1,076,052,000	4,202,628,000	3,969,293,000	4,240,802,000		50,000,000
Estimated City of Seattle's claim for refunds not including interest												$ 28,000,000
Number of factors considered in assessment												2