Commitments and Contingencies, Unrecorded Unconditional Purchase Obligation and Loss Contingencies (Details) (USD $)	Mar. 31, 2012	Mar. 31, 2010	Mar. 31, 2012 Native Village of Kivalina vs. Xcel Energy Inc. et al. [Member]	Feb. 28, 2008 Native Village of Kivalina vs. Xcel Energy Inc. et al. [Member]	Mar. 31, 2012 Comer vs. Xcel Energy Inc. et al. [Member]	May 31, 2011 Comer vs. Xcel Energy Inc. et al. [Member]	Mar. 31, 2012 Merricourt Wind Project Litigation [Member]	May 31, 2011 Merricourt Wind Project Litigation [Member]	Apr. 30, 2011 Merricourt Wind Project Litigation [Member] MW	Mar. 31, 2011 Merricourt Wind Project Litigation [Member]	Mar. 31, 2012 NSP-Minnesota [Member]	Mar. 31, 2012 NSP-Minnesota [Member] Capital Commitments [Member] CSAPR [Member]	Mar. 31, 2012 SPS [Member] Capital Commitments [Member] CSAPR [Member] Y	Mar. 31, 2012 NSP-Wisconsin [Member] Capital Commitments [Member] CSAPR [Member]
Other Environmental Requirements [Abstract]
Number of regulations in New Mexico to limit GHG emissions which were repealed in 2012	2
Estimated costs to comply with the Cross-State Air Pollution Rule (CSAPR)												$ 10,000,000	$ 470,000,000	$ 200,000
Number of years in which capital expenditures are expected to be incurred (in years)													4
Number of environmental groups who petitioned the U.S. Department of the Interior		2
Number of coal-fired boilers in Colorado		12
Number of coal-fired cement kilns in Colorado		1
Estimated cost for meeting the BART and other CAA requirements											50,000,000
Estimated amount spent on projects to reduce NOx emissions on Sherco Units 1 and 2											20,000,000
Environmental Litigation [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
Employment, Tort and Commercial Litigation [Abstract]
Generating capacity (in MW)									150
Merricourt deposit										101,000,000
Minimum amount of damages claimed by plaintiff								$ 240,000,000