Rate Matters Rate Matters (Details) $ in Thousands			1 Months Ended					3 Months Ended			9 Months Ended		12 Months Ended
	Oct. 20, 2015	Oct. 01, 2015 USD ($)	Sep. 30, 2015	May. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Feb. 28, 2015	Nov. 30, 2013	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) MW	Sep. 30, 2014 USD ($)	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	$ 0
FERC Proceeding, MISO ROE Complaint [Member] | Federal Energy Regulatory Commission (FERC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Number Of Steps Required For Newly Adopted ROE Discounted Cash Flow Methodology											2
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 [Member]
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 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Base Return On Equity Charged To Customers Through Transmission Formula Rates							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%
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Lower Bound, Percentage			8.72%								8.67%
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Upper Bound, Percentage			9.13%								9.54%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member] | Federal Energy Regulatory Commission (FERC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Basis Point Adder Requested By Third Parties											50
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member] | FERC Staff [Member]
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											8.68%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member] | MISO TOs [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Lower Bound, Percentage											10.80%
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
NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 - Electric Rates 2016 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 27,400
Public Utilities, Requested Rate Increase (Decrease), Percentage				3.90%
Public Utilities, Requested Rate Base, Amount				$ 1,200,000
NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 - Gas Rates 2016 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 5,900
Public Utilities, Requested Rate Increase (Decrease), Percentage				5.00%
Public Utilities, Requested Rate Base, Amount				$ 111,200
NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage				10.20%
Public Utilities, Requested Equity Capital Structure, Percentage				52.50%
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
Minimum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Facility Generating Capacity, In MW | MW											600
Minimum | NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Decrease In Transmission Revenue, Net Of Expense, Due To New ROE Methodology											$ 7,000
Maximum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Facility Generating Capacity, In MW | MW											671
Maximum | NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Decrease In Transmission Revenue, Net Of Expense, Due To New ROE Methodology											$ 9,000
Subsequent Event | NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member] | MISO TOs [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Lower Bound, Percentage	10.75%
Subsequent Event | NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 - Electric Rates 2016 [Member] | Public Service Commission of Wisconsin (PSCW) [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Recommended Rate Increase (Decrease), Amount		$ 10,400
Public Utilities, Recommended Rate Increase, Percentage		1.50%
Subsequent Event | NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 - Gas Rates 2016 [Member] | Public Service Commission of Wisconsin (PSCW) [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Recommended Rate Increase (Decrease), Amount		$ 3,000
Public Utilities, Recommended Rate Increase, Percentage		2.50%
Subsequent Event | NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 [Member] | Public Service Commission of Wisconsin (PSCW) [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Recommended Return on Equity, Percentage		10.00%
Public Utilities, Recommended Equity Capital Structure, Percentage		52.50%
Subsequent Event | NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 [Member] | Citizens Utility Board [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage		8.75%