Rate Matters Rate Matters (Details) - USD ($) $ in Thousands	1 Months Ended							6 Months Ended
	May 31, 2018	Mar. 31, 2018	Nov. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Feb. 28, 2015	Nov. 30, 2013	Jun. 30, 2018
Public Service Commission of Wisconsin (PSCW) [Member] | PSCW Proceeding - Tax Cuts and Jobs Act of 2017 [Member]
Public Utilities, General Disclosures [Line Items]
Tax Cuts and Jobs Act of 2017, Approved Refund of 2018 TCJA Benefits	$ 27,000
Tax Cuts and Jobs Act of 2017, Approved Deferral of 2018 TCJA Benefits	$ 5,000
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%