Rate Matters Rate Matters (Details)				1 Months Ended							3 Months Ended			9 Months Ended		12 Months Ended
	Oct. 26, 2016 USD ($)	Sep. 28, 2016	Jun. 30, 2016	Oct. 31, 2016 USD ($)	Aug. 31, 2016 USD ($)	Jul. 31, 2016 USD ($)	Apr. 30, 2016 USD ($)	Mar. 31, 2015 USD ($)	Feb. 28, 2015	Nov. 30, 2013	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 MW	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($)
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project											$ 0	$ 0		$ 0	$ 5,237,000
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount							$ 17,400,000
Public Utilities, Requested Rate Increase (Decrease), Percentage							2.40%
Public Utilities, Requested Rate Base, Amount							$ 1,188,000,000
Public Utilities, Requested Increase Related to Rate Base Investments							11,000,000
Public Utilities, Requested Increase Related to Generation and Transmission Expenses							6,800,000
Public Utilities, Requested Increase Related to Fuel and Purchased Power Expenses							11,000,000
Public Utilities, Total Requested Rate Increase Excluding Refunds							28,800,000
Public Utilities, Requested Decrease Related to Fuel Refunds							(9,500,000)
Public Utilities, Requested Decrease Related to Settlement Refund							(1,900,000)
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017 | Public Service Commission of Wisconsin (PSCW) Staff [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 19,500,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					2.70%
Public Utilities, Difference Between Filed Request and PSCW Staff Recommendation					$ 7,400,000
Public Utilities, Requested Increase Related to Rate Base Investments					7,600,000
Public Utilities, Requested Increase Related to Generation and Transmission Expenses					6,100,000
Public Utilities, Requested Increase Related to Fuel and Purchased Power Expenses					7,700,000
Public Utilities, Total Requested Rate Increase Excluding Refunds					21,400,000
Public Utilities, Requested Decrease Related to Fuel Refunds					0
Public Utilities, Requested Decrease Related to Settlement Refund					(1,900,000)
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017 | Public Service Commission of Wisconsin (PSCW)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Adjustment to Rate Request Related to Fuel Refund						$ 9,500,000
Public Utilities, Revised Requested Rate Increase, Amount						$ 29,900,000
Public Utilities, Revised Requested Rate Increase, Percentage						4.20%
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Gas Rates 2017
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount							$ 4,800,000
Public Utilities, Requested Rate Increase (Decrease), Percentage							3.90%
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Gas Rates 2017 | Public Service Commission of Wisconsin (PSCW) Staff [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 4,800,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					3.90%
NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage							10.00%
Public Utilities, Percentage of Excess Earnings to be Refunded due to Earnings Cap							100.00%
NSP-Wisconsin | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Loss on Monticello life cycle management/extended power uprate project													$ 5,000,000
NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Nuclear Project Expenditures, Amount																	$ 665,000,000
Total Capitalized Nuclear Project Costs																	$ 748,000,000
Initial Estimated Nuclear Project Expenditures																		$ 320,000,000
NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation | Minnesota Public Utilities Commission
Public Utilities, General Disclosures [Line Items]
Public Utilities, Amount Of Recoverable Investment, With Return								$ 415,000,000
Public Utilities, Amount Of Recoverable Investment, Without A Return								$ 333,000,000
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 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 | FERC Proceeding, MISO ROE Complaint | Administrative Law Judge
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%
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint | MPUC, NDPSC, SDPUC, and DOC
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 Proceeding, MISO ROE Complaint | FERC Staff
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 | FERC Proceeding, MISO ROE Complaint | MISO TOs
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 | FERC Proceeding, MISO ROE Complaint | Federal Energy Regulatory Commission (FERC)
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
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													$ 129,000,000
Minimum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW																600
Maximum | NSP-Minnesota | MPUC Proceeding - Nuclear Project Prudency Investigation
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW																671
Subsequent Event [Member] | NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017 | Public Service Commission of Wisconsin (PSCW)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 22,500,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	3.20%
Public Utilities, Approved Increase Related to Rate Base Investments	$ 7,600,000
Public Utilities, Approved Increase Related to Generation and Transmission Expenses	6,100,000
Public Utilities, Approved Increase Related to Fuel and Purchased Power Expenses	10,700,000
Public Utilities, Total Approved Rate Increase, Excluding Refunds	24,400,000
Public Utilities, Approved Decrease Related to Fuel Refunds	0
Public Utilities, Approved Decrease Related to Settlement Refund	(1,900,000)
Subsequent Event [Member] | NSP-Wisconsin | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Gas Rates 2017 | Public Service Commission of Wisconsin (PSCW)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 4,800,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	3.90%
Subsequent Event [Member] | NSP-Wisconsin | MPSC Proceeding - Michigan 2017 Natural Gas Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 347,000
Public Utilities, Requested Rate Increase (Decrease), Percentage				6.50%
Public Utilities, Requested Rate Base, Amount				$ 6,400,000
Public Utilities, Requested Return on Equity, Percentage				10.20%
Public Utilities, Requested Equity Capital Structure, Percentage				52.56%
Public Utilities, Requested Rider Revenue, Amount				$ 129,000
Public Utilities, Requested Rider Revenue, Percentage				2.40%