Commitments and Contingencies, Legal Contingencies (Details) (USD $)	3 Months Ended		9 Months Ended						9 Months Ended	14 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Native Village of Kivalina vs. Xcel Energy Inc. et al. [Member]	Feb. 29, 2008 Native Village of Kivalina vs. Xcel Energy Inc. et al. [Member]	Sep. 30, 2012 Comer vs. Xcel Energy Inc. et al. [Member]	May 31, 2011 Comer vs. Xcel Energy Inc. et al. [Member]	Sep. 30, 2012 Pacific Northwest FERC Refund Proceeding [Member]	Jun. 30, 2001 Pacific Northwest FERC Refund Proceeding [Member]
Legal Contingencies [Abstract]
Number of other entities against which the native village of Kivalina has filed a lawsuit						23
Estimated cost of relocating the village of Kivalina, low end of range					$ 95,000,000
Estimated cost of relocating the village of Kivalina, high end of range					400,000,000
Accrual for legal contingency					0		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	992,287,000	1,063,934,000	2,937,840,000	3,141,481,000						50,000,000
Estimated City of Seattle's claim for refunds not including interest									$ 28,000,000
Number of factors considered in assessment									2