Rate Matters Rate Matters (Details) - USD ($) $ in Thousands	1 Months Ended						3 Months Ended
	Mar. 31, 2017	Oct. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Feb. 28, 2015	Nov. 30, 2013	Mar. 31, 2017
NSP-Wisconsin | MPSC Proceeding - Michigan 2017 Natural Gas Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 347
Public Utilities, Requested Rate Increase (Decrease), Percentage		6.50%
Public Utilities, Requested Return on Equity, Percentage		10.20%
Public Utilities, Requested Equity Capital Structure, Percentage		52.56%
Public Utilities, Requested Rate Base, Amount		$ 6,400
Public Utilities, Requested Rider Revenue, Amount		$ 129
Public Utilities, Requested Rider Revenue, Percentage		2.40%
NSP-Wisconsin | MPSC Staff | MPSC Proceeding - Michigan 2017 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	52.56%
NSP-Wisconsin | MPSC Staff | MPSC Proceeding - Michigan 2017 Natural Gas Rate Case, Rates 2017 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Rate Increase Under the Settlement	$ 266
Public Utilities, Rate Increase Under the Settlement, Percentage	5.00%
NSP-Wisconsin | MPSC Staff | MPSC Proceeding - Michigan 2017 Natural Gas Rate Case, Rates 2018 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Rate Increase Under the Settlement	$ 140
Public Utilities, Rate Increase Under the Settlement, Percentage	2.50%
NSP-Wisconsin | MPSC Staff | MPSC Proceeding - Michigan 2017 Natural Gas Rate Case, Rates 2019 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Rate Increase Under the Settlement	$ 143
Public Utilities, Rate Increase Under the Settlement, Percentage	2.50%
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%
Public Utilities, Maximum Equity Capital Structure Percentage Allowed Per The Complaint						50.00%
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 | MPUC, NDPSC, SDPUC, and DOC | 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							8.81%
NSP-Minnesota | FERC Staff | 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							8.78%
NSP-Minnesota | MISO TOs | 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							10.92%
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%