Rate Matters Rate Matters (Details) $ in Thousands			1 Months Ended						3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jan. 06, 2015	Jul. 31, 2016 USD ($)	Apr. 30, 2016 USD ($)	Dec. 31, 2015	Mar. 31, 2015 USD ($)	Feb. 28, 2015	Nov. 30, 2013	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 MW	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($)
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project									$ 0	$ 0		$ 0	$ 5,237
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 17,400
Public Utilities, Requested Rate Increase (Decrease), Percentage				2.40%
Public Utilities, Requested Increase Related to Rate Base Investments				$ 11,000
Public Utilities, Requested Increase Related to Generation and Transmission Expenses				6,800
Public Utilities, Requested Increase Related to Fuel and Purchased Power Expenses				11,000
Public Utilities, Total Requested Rate Increase Excluding Refunds				28,800
Public Utilities, Requested Decrease Related to Fuel Refunds				(9,500)
Public Utilities, Requested Decrease Related to Settlement Refund				(1,900)
Public Utilities, Requested Rate Base, Amount				1,188,000
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Gas Rates 2017
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 4,800
Public Utilities, Requested Rate Increase (Decrease), Percentage				3.90%
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage				10.00%
Public Utilities, Percentage of Excess Earnings to be Refunded due to Earnings Cap				100.00%
NSP-Wisconsin | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project											$ 5,000
NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Nuclear Project Expenditures, Amount															$ 665,000
Total Capitalized Nuclear Project Costs															$ 748,000
Initial Estimated Nuclear Project Expenditures																$ 320,000
NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation | Minnesota Public Utilities Commission
Public Utilities, General Disclosures [Line Items]
Public Utilities, Amount Of Recoverable Investment, With Return						$ 415,000
Public Utilities, Amount Of Recoverable Investment, Without A Return						$ 333,000
Public Utilities, Percentage Of Investment Considered Used And Useful						50.00%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint
Public Utilities, General Disclosures [Line Items]
Public Utilities, Base Return On Equity Charged To Customers Through Transmission Formula Rates							12.38%	12.38%
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties							8.67%	9.15%
Public Utilities, Maximum Equity Capital Structure Percentage Allowed Per The Complaint								50.00%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint | Administrative Law Judge
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties	9.70%				10.32%
Public Utilities, Length of Refund Period, Recommended by Third Parties	15 months
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint | MPUC, NDPSC, SDPUC, and DOC
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Upper Bound, Percentage												8.82%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Lower Bound, Percentage												8.81%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint | FERC Staff
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties												8.78%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint | MISO TOs
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties												10.92%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint | Federal Energy Regulatory Commission (FERC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Basis Point Adder Requested By Third Parties		50
Xcel Energy Inc. | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project											$ 129,000
Minimum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW														600
Minimum | NSP-Minnesota | FERC Proceeding, MISO ROE Complaint
Public Utilities, General Disclosures [Line Items]
Public Utilities, Decrease In Transmission Revenue, Net Of Expense, Due To New ROE Methodology												$ 8,000
Maximum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW														671
Maximum | NSP-Minnesota | FERC Proceeding, MISO ROE Complaint
Public Utilities, General Disclosures [Line Items]
Public Utilities, Decrease In Transmission Revenue, Net Of Expense, Due To New ROE Methodology												$ 10,000
Subsequent Event [Member] | NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017 | Public Service Commission of Wisconsin (PSCW)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Revised Requested Rate Increase, Amount			$ 26,900
Public Utilities, Revised Requested Rate Increase, Percentage			3.80%