Rate Matters, NSP-Minnesota (Details) (USD $)	3 Months Ended		0 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended				0 Months Ended	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 06, 2015		Nov. 30, 2013	Dec. 31, 2014	Jan. 31, 2015	Jun. 30, 2014	Oct. 31, 2014	Feb. 28, 2015	Mar. 26, 2015	Dec. 31, 2013	Nov. 30, 2014	Dec. 31, 2014
Rate Matters [Abstract]
Loss on Monticello LCM/EPU project	$ 129,463,000	$ 0
Xcel Energy Inc. | MPUC Proceeding - Nuclear Project Prudency Investigation
Rate Matters [Abstract]
Public Utilities, Reduction in revenue requirement			25,000,000
Public Utilities, Reduction in pre-tax income			16,000,000	[1]
NSP-Minnesota | MPUC Proceeding - Minnesota Electric Rate Case 2014
Rate Matters [Abstract]
Public Utilities, number of years rate case is applicable for (in years)					2 years
Public Utilities, Requested Return on Equity, Percentage					10.25%
Public Utilities, Requested Equity Capital Structure, Percentage					52.50%
Amount of public utility's amended unadjusted cumulative multi-year rate increase (decrease)						221,300,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU costs						0
Amount of public utility's amended estimated adjusted cumulative multi-year increase (decrease)						221,300,000
Public Utilities, Number of proposals regarding potential refund for interim rates						2
Public Utilities, length of netting period for any potential refund/surcharge that could occur when final rates are established						2 years
NSP-Minnesota | MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]
Rate Matters [Abstract]
Public Utilities, Requested Rate Base, Amount					6,670,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					192,700,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					6.90%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						115,300,000
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to an increase to sales forecast						(38,500,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to a lower return on equity						0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU costs						(12,200,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to property taxes						(13,200,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to amortization of Prairie Island EPU costs						(5,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to health care, pension and other benefits						(1,900,000)
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to other costs						(6,500,000)
NSP-Minnesota | MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]
Rate Matters [Abstract]
Public Utilities, Requested Rate Base, Amount					412,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					98,000,000	98,500,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					3.50%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						106,000,000
Amount of public utility's amended unadjusted cumulative multi-year rate increase (decrease)						221,300,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU costs						11,700,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to property taxes						(3,300,000)
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to other costs						1,700,000
Public Utilities, Adjustment to requested rate increase (decrease) by public utility related to depreciation expense						0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to PTCs moving to base rates						(11,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to DOE settlement proceeds						10,100,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to emission chemicals						(1,600,000)
NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Rate Matters [Abstract]
Costs for nuclear project, Amount	665,000,000
Total capitalized nuclear project costs	748,000,000
Initial estimated nuclear project costs	320,000,000
Loss on Monticello LCM/EPU project	129,000,000
NSP-Minnesota | SDPUC Proceeding - South Dakota Electric Rate Case 2015
Rate Matters [Abstract]
Public Utilities, Requested Return on Equity, Percentage								10.25%
Public Utilities, Requested Equity Capital Structure, Percentage								53.86%
Public Utilities, Requested Rate Base, Amount								433,200,000
Public Utilities, Requested Rate Increase (Decrease), Amount								15,600,000
Public Utilities, Requested Rate Increase (Decrease), Percentage								8.00%
Public Utilities, Interim Rate Increase (Decrease), Amount							15,600,000
Public Utilities, Rider costs to be recovered through base rates, Amount								9,000,000
NSP-Minnesota | MPUC Proceeding - Transmission Cost Recovery Rider Filing 2015 [Member]
Rate Matters [Abstract]
Public Utilities, Projected incremental revenue from rider in 2015									65,800,000
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member]
Rate Matters [Abstract]
Public Utilities, ROE applicable to transmission formula rates in the MISO region, upper bound					12.38%
Public Utilities, ROE applicable to transmission formula rates in the MISO region, lower bound					9.15%
Public Utilities, maximum equity capital structure percentage allowed per the complaint					50.00%
Public Utilities, Incremental ROE basis point increase (decrease) recommended by third parties										50
Public Utilities, ROE applicable to transmission formula rates in the MISO region, recommended by third parties										8.67%
NSP-Minnesota | Minnesota Public Utilities Commission [Member] | MPUC Proceeding - Minnesota Electric Rate Case 2014
Rate Matters [Abstract]
Public Utilities, Approved Rate Increase (Decrease), Amount											168,000,000
Public Utilities, Approved Rate Increase (Decrease), Percentage											6.10%
Public Utilities, Approved Return on Equity, Percentage											9.72%
Public Utilities, Approved Equity Capital Structure, Percentage											52.50%
Public Utilities; Approved adjustment to requested rate increase (decrease) related to Monticello EPU costs											(18,200,000)
Public Utilities, Unadjusted cumulative multi-year increase (decrease), approved.											185,800,000
Public Utilities, Estimated adjusted cumulative multi-year increase (decrease), approved.											167,600,000
Public Utilities, number of years of full revenue decoupling pilot for the residential and small commercial and industrial (C&I) class											3 years
Public Utilities, amount of percent cap on base revenue for three year revenue decoupling pilot for the residential and small commercial and industrial (C&I) class											3.00%
NSP-Minnesota | Minnesota Public Utilities Commission [Member] | MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount					192,700,000
Public Utilities, Interim Rate Increase (Decrease), Amount												127,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount											58,100,000
Public Utilities, approved excess depreciation reserve utilization											50.00%
Public Utilities, Approved adjustment to requested rate increase (decrease) related to an increase to sales forecast											(38,500,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to a lower return on equity											(31,900,000)
Public Utilities; Approved adjustment to requested rate increase (decrease) related to Monticello EPU costs											(37,600,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to property taxes											(13,200,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to amortization of Prairie Island EPU costs											(5,100,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to health care, pension and other benefits											(3,000,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to other costs											(5,300,000)
NSP-Minnesota | Minnesota Public Utilities Commission [Member] | MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount					98,500,000
Public Utilities, Rate increase (decrease) recommended by third parties											127,700,000
Public Utilities, approved excess depreciation reserve utilization											30.00%
Public Utilities; Approved adjustment to requested rate increase (decrease) related to Monticello EPU costs											35,400,000
Public Utilities, Approved adjustment to requested rate increase (decrease) related to property taxes											(3,300,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to other costs											200,000
Public Utilities, Approved adjustment to requested rate increase (decrease) related to depreciation expense											(500,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to PTCs moving to base rates											(11,100,000)
Public Utilities, Approved adjustment to requested rate increase (decrease) related to DOE settlement proceeds											10,100,000
Public Utilities, Approved adjustment to requested rate increase (decrease) related to emission chemicals											(1,600,000)
NSP-Minnesota | Minnesota Public Utilities Commission [Member] | MPUC Proceeding - Electric Rate Case 2014, Rates 2016 [Member]
Rate Matters [Abstract]
Public Utilities, approved excess depreciation reserve utilization											20.00%
NSP-Minnesota | Minnesota Public Utilities Commission [Member] | MPUC Proceeding - Nuclear Project Prudency Investigation
Rate Matters [Abstract]
Public Utilities, Amount of recoverable investment, with return			415,000,000
Amount of recoverable investment, without a return			333,000,000
Public Utilities, Percentage of investment considered used and useful			50.00%
NSP-Minnesota | Minnesota Department of Commerce [Member] | MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]
Rate Matters [Abstract]
Public Utilities, approximate increase (decrease) in revenues (per month) under alternative option											(3,500,000)
NSP-Minnesota | Federal Energy Regulatory Commission (FERC) | FERC Proceeding, MISO ROE Complaint [Member]
Rate Matters [Abstract]
Public Utilities, number of steps required for newly adopted ROE discounted cash flow methodology								2
Public Utilities, Incremental ROE basis point increase (decrease) recommended by third parties													50
NSP-Minnesota | Administrative Law Judge [Member] | MPUC Proceeding - Minnesota Electric Rate Case 2014
Rate Matters [Abstract]
Public utilities, ROE recommended by third parties														9.77%
Public Utilities, Equity capital structure recommended by third parties														52.50%
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to Monticello EPU costs														0
Public Utilities, Unadjusted cumulative multi-year increase (decrease) recommended by third parties.														191,500,000
Public Utilities, Estimated adjusted cumulative multi-year increase (decrease) recommended by third parties.														191,500,000
NSP-Minnesota | Administrative Law Judge [Member] | MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount					192,700,000
Amount of the rate increase (decrease) recommended by third parties, adjusted.														69,100,000
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to an increase to sales forecast														(38,500,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to a lower return on equity														(28,400,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to Monticello EPU costs														(31,300,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to property taxes														(13,200,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to amortization of Prairie Island EPU costs														(5,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to health care, pension and other benefits														(1,900,000)
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to other costs														(5,200,000)
Amount of the rate increase (decrease) recommended by third parties, unadjusted.														69,100,000
NSP-Minnesota | Administrative Law Judge [Member] | MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount					98,500,000
Public Utilities, Rate increase (decrease) recommended by third parties														122,400,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to Monticello EPU costs														29,100,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to property taxes														(3,300,000)
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to other costs														700,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to depreciation expense														0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to PTCs moving to base rates														(11,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to DOE settlement proceeds														10,100,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to emission chemicals														(1,600,000)
Minimum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Rate Matters [Abstract]
Facility generating capacity (in MW)	600
Minimum | NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member]
Rate Matters [Abstract]
Public Utilities, Increase (decrease) in transmission revenue, net of expense, due to the new ROE methodology						(7,000,000)
Maximum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Rate Matters [Abstract]
Facility generating capacity (in MW)	671
Maximum | NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member]
Rate Matters [Abstract]
Public Utilities, Increase (decrease) in transmission revenue, net of expense, due to the new ROE methodology						(9,000,000)
Minnesota Jurisdiction [Member] | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Rate Matters [Abstract]
Public Utilities, Reduction in revenue requirement			18,000,000
Public Utilities, Reduction in pre-tax income			$ 12,000,000	[1]

[1] Pre-tax income reflects the net impact of the reductions in revenue and depreciation expense.