Commitments and Contingencies, Legal Contingencies (Details) (USD $)	3 Months Ended		9 Months Ended				9 Months Ended	13 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Comer vs. Xcel Energy Inc. et al. [Member]	May 31, 2011 Comer vs. Xcel Energy Inc. et al. [Member] Counterparty	Sep. 30, 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		$ 0
Minimum number of utility, oil, chemical and coal companies against which a lawsuit was filed in U.S. District Court in Mississippi						85
Minimum amount of damages claimed by plaintiff							34,000,000
Sales to the City of Seattle	1,044,300,000	992,287,000	3,128,186,000	2,937,840,000				50,000,000
Estimated City of Seattle's claim for refunds not including interest							$ 28,000,000
Number of factors considered in assessment							2