Rate Matters Rate Matters (Details) (USD $)	3 Months Ended		1 Months Ended		0 Months Ended	1 Months Ended				12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Nov. 30, 2013	Jun. 30, 2014	Mar. 06, 2015	Feb. 28, 2015	Nov. 30, 2014	Mar. 31, 2015	Oct. 31, 2014	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project	$ 5,237,000	$ 0
FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
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%
FERC Proceeding, MISO ROE Complaint [Member] | Federal Energy Regulatory Commission (FERC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, number of steps required for newly adopted ROE discounted cash flow methodology				2
NSP Minnesota [Member] | Nuclear Project Prudency Investigation [Member] [Member]
Public Utilities, General Disclosures [Line Items]
Nuclear project expenditures, Amount	665,000,000
Total capitalized nuclear project costs	748,000,000
Initial estimated nuclear project expenditures	320,000,000
NSP Minnesota [Member] | Nuclear Project Prudency Investigation [Member] [Member] | Minnesota Public Utilities Commission [Member]
Public Utilities, General Disclosures [Line Items]
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 [Member] | FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
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 [Member] | FERC Proceeding, MISO ROE Complaint [Member] | Federal Energy Regulatory Commission (FERC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Incremental ROE basis point increase (decrease) recommended by third parties							50
Xcel Energy Inc. | Nuclear Project Prudency Investigation [Member] [Member]
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project	129,000,000
NSP-Wisconsin | Nuclear Project Prudency Investigation [Member] [Member]
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project	5,000,000
NSP-Wisconsin | MPSC Proceeding - Electric Rate Case 2015 [Member] | Michigan Public Service Commission (MPSC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount									900,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									6.10%
Public Utilities, Requested Return on Equity, Percentage									10.30%
Public Utilities, Requested Equity Capital Structure, Percentage									52.59%
Public Utilities, Requested Rate Base, Amount									35,200,000
Public Utilities, Approved Return on Equity, Percentage								10.10%
NSP-Wisconsin | MPSC Proceeding - Electric Rate Case 2015, Electric Rates 2016 | Michigan Public Service Commission (MPSC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount									289,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									1.90%
Public Utilities, Approved Rate Increase (Decrease), Amount								289,000
Public Utilities, Approved Rate Increase (Decrease), Percentage								2.00%
NSP-Wisconsin | MPSC Proceeding - Electric Rate Case 2015, Electric Rates 2015 [Member] | Michigan Public Service Commission (MPSC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount								720,000
Public Utilities, Approved Rate Increase (Decrease), Percentage								4.90%
Minimum | FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Increase (decrease) in transmission revenue, net of expense, due to the new ROE methodology										(7,000,000)
Minimum | NSP Minnesota [Member] | Nuclear Project Prudency Investigation [Member] [Member]
Public Utilities, General Disclosures [Line Items]
Facility generating capacity (in MW)	600
Maximum | FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Increase (decrease) in transmission revenue, net of expense, due to the new ROE methodology										$ (9,000,000)
Maximum | NSP Minnesota [Member] | Nuclear Project Prudency Investigation [Member] [Member]
Public Utilities, General Disclosures [Line Items]
Facility generating capacity (in MW)	671