Rate Matters Rate Matters (Details) - USD ($) $ in Thousands	1 Months Ended						3 Months Ended
	Mar. 31, 2018	Nov. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Feb. 28, 2015	Nov. 30, 2013	Mar. 31, 2018
NSP-Wisconsin | MPSC Proceeding - Michigan 2018 Electric Rate Case [Member]
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 Rate Base, Amount		$ 43,000
Public Utilities, Requested Equity Capital Structure, Percentage		52.50%
NSP-Wisconsin | MPSC Staff [Member] | MPSC Proceeding - Michigan 2018 Electric Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage	9.80%
Public Utilities, Rate Increase Under the Settlement	$ 300
Public Utilities, Rate Increase Under the Settlement, Percentage	2.00%
Public Utilities, Requested Equity Capital Structure, Percentage	52.50%
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%
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%
Public Utilities, Length of Refund Period, In Months			15 months
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 Regional Transmission Operator's Region, Recommended By Third Parties				9.70%