Rate Matters (Details) $ in Thousands		1 Months Ended						3 Months Ended	12 Months Ended
	Jan. 06, 2015	Jan. 31, 2016	Dec. 31, 2015 USD ($)	May. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Feb. 28, 2015	Nov. 30, 2013	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) MW	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($)
Public Utilities, General Disclosures [Line Items]
Loss on Monticello LCM/EPU project									$ 5,237	$ 0	$ 0
NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 - Gas Rates 2016
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
Public Utilities, Percentage of Requested Non-fuel and Purchased Power Rate Increase Approved by Commission			71.00%
Public utilities, Requested Increase Related To Capital Investment				3,700
Public Utilities, Requested Decrease Related to ROE and Capital Structure				0
Public Utilities, Requested Increase Related to Operating and Maintenance Expenses				3,200
Public Utilities, Requested Decrease Related to Sales Forecast				(3,900)
Public Utilities, Requested Increase Related Environmental Remediation Expenses				$ 2,900
NSP-Wisconsin | PSCW Proceeding - Electric and Gas Rate Case 2016 - Gas Rates 2016 | Public Service Commission of Wisconsin (PSCW) [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 4,200
Public Utilities, Approved Rate Increase (Decrease), Percentage			3.60%
Public utilities, Approved Increase Related To Capital Investment			$ 3,700
Public Utilities, Approved Decrease Related to ROE and Capital Structure			(400)
Public Utilities, Approved Increase Related to Operating and Maintenance Expenses			1,900
Public Utilities, Approved Decrease Related to Sales Forecast			3,900
Public Utilities, Approved Increase Related Environmental Remediation Expenses			$ 2,900
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 | PSCW Proceeding - Electric and Gas Rate Case 2016 [Member] | Public Service Commission of Wisconsin (PSCW) [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage			10.00%
Public Utilities, Approved Equity Capital Structure, Percentage			52.50%
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
Public Utilities, Percentage of Requested Non-fuel and Purchased Power Rate Increase Approved by Commission			65.00%
Public utilities, Requested Increase Related To Capital Investment				23,000
Public Utilities, Requested Decrease Related to ROE and Capital Structure				0
Public Utilities, Requested Increase Related to Generation and Transmission Expenses				37,200
Public Utilities, Requested Increase Related to Operating and Maintenance Expenses				11,100
Public Utilities, Requested Decrease Related to Sales Forecast				(27,000)
Public Utilities, Total Requested Rate Increase Excluding Fuel and Purchased Power				44,300
Public Utilities, Requested Decrease Related to Fuel and Purchased Power Expenses				$ (16,900)
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, Approved Rate Increase (Decrease), Amount			$ 7,600
Public Utilities, Approved Rate Increase (Decrease), Percentage			1.10%
Public utilities, Approved Increase Related To Capital Investment			$ 13,900
Public Utilities, Approved Decrease Related to ROE and Capital Structure			(3,800)
Public Utilities, Approved Increase Related to Operating and Maintenance Expenses			42,700
Public Utilities, Approved Increase Related to Operating and Maintenance Expenses			3,200
Public Utilities, Approved Decrease Related to Sales Forecast			27,000
Public Utilities, Total Approved Rate Increase Excluding Fuel and Purchased Power			29,000
Public Utilities, Approved Decrease Related to Fuel and Purchased Power Expenses			$ 21,400
NSP-Wisconsin | Nuclear Project Prudency Investigation [Member]
Public Utilities, General Disclosures [Line Items]
Loss on Monticello LCM/EPU project								$ 5,000
NSP-Wisconsin | FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE applicable to transmission formula rates in the MISO region, upper bound, percentage							12.38%
Public Utilities, ROE applicable to transmission formula rates in the MISO 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 MISO Region, Lower Bound, Percentage									8.67%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Upper Bound, Percentage									9.54%
NSP-Wisconsin | FERC Proceeding, MISO ROE Complaint [Member] | Federal Energy Regulatory Commission (FERC) [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, number of steps required for newly adopted ROE discounted cash flow methodology									2
Public Utilities, Incremental ROE basis point increase (decrease) recommended by third parties	50
NSP-Wisconsin | 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 MISO region, recommended by third parties									8.68%
NSP-Wisconsin | 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 MISO Region, Lower Bound, Percentage									10.80%
NSP-Wisconsin | FERC Proceeding, MISO ROE Complaint [Member] | Administrative Law Judge [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE applicable to transmission formula rates in the MISO region, recommended by third parties			10.32%
NSP-Minnesota | Nuclear Project Prudency Investigation [Member]
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 | Nuclear Project Prudency Investigation [Member] | 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%
Xcel Energy Inc. | Nuclear Project Prudency Investigation [Member]
Public Utilities, General Disclosures [Line Items]
Loss on Monticello LCM/EPU project								$ 129,000
Minimum | NSP-Wisconsin | 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									$ 8,000
Minimum | NSP-Minnesota | Nuclear Project Prudency Investigation [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW									600
Maximum | NSP-Wisconsin | 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									$ 10,000
Maximum | NSP-Minnesota | Nuclear Project Prudency Investigation [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Facility Generating Capacity, In MW | MW									671
Subsequent Event | NSP-Wisconsin | FERC Proceeding, MISO ROE Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Lower Bound, Percentage		8.72%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Upper Bound, Percentage		9.32%
Subsequent Event | NSP-Wisconsin | 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 MISO region, recommended by third parties		8.78%
Subsequent Event | NSP-Wisconsin | 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 MISO region, recommended by third parties		10.96%