Rate Matters Rate Matters (Details) $ in Thousands	1 Months Ended								3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($)	May 31, 2017 USD ($)	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Feb. 28, 2015	Nov. 30, 2013	Mar. 31, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) MW	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($)
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project										$ 0	$ 0	$ 5,237
Xcel Energy Inc. | Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project									$ 129,000
NSP-Wisconsin | MPSC Proceeding - Michigan 2018 Electric Rate Case
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 1,000
Public Utilities, Requested Rate Increase (Decrease), Percentage		7.10%
Public Utilities, Requested Return on Equity, Percentage		10.10%
Public Utilities, Requested Equity Capital Structure, Percentage		52.50%
Public Utilities, Requested Rate Base, Amount		$ 43,000
NSP-Wisconsin | Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project									5,000
NSP-Wisconsin | Public Service Commission of Wisconsin (PSCW) | PSCW Proceeding - Wisconsin 2018 Electric and Natural Gas Rate Case - Electric Rates 2018 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 25,000
Public Utilities, Requested Rate Increase (Decrease), Percentage			3.60%
Public Utilities, Requested Rate Base, Amount			$ 1,200,000
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 9,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	1.40%
NSP-Wisconsin | Public Service Commission of Wisconsin (PSCW) | PSCW Proceeding - Wisconsin 2018 Electric and Natural Gas Rate Case - Gas Rates 2018 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 12,000
Public Utilities, Requested Rate Increase (Decrease), Percentage			10.10%
Public Utilities, Requested Rate Base, Amount			$ 138,000
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 10,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	8.30%
NSP-Wisconsin | Public Service Commission of Wisconsin (PSCW) | PSCW Proceeding - Wisconsin 2018 Electric and Natural Gas Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage			10.00%
Public Utilities, Requested Equity Capital Structure, Percentage			52.53%
Public Utilities, Approved Return on Equity, Percentage	9.80%
Public Utilities, Approved Equity Capital Structure, Percentage	51.45%
NSP-Minnesota | 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
Loss on Monticello life cycle management/extended power uprate project									$ 129,000
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 MISO Region, Recommended by Third Parties							8.67%	9.15%
NSP-Minnesota | Minnesota Public Utilities Commission | Nuclear Project Prudency Investigation
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
NSP-Minnesota | Federal Energy Regulatory Commission (FERC) | FERC Proceeding, MISO ROE Complaint
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Approved	10.32%			10.32%		10.32%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, with RTO Adder, Approved										10.82%
Public Utilities, ROE Basis Point Adder, Approved										50
NSP-Minnesota | Administrative Law Judge | FERC Proceeding, MISO ROE Complaint
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable to Transmission Formula Rates in the MISO Region, Recommended by Third Parties					9.70%
Minimum | NSP-Minnesota | Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW												600
Maximum | NSP-Minnesota | Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW												671