Rate Matters Rate Matters (Details) $ in Thousands		1 Months Ended						3 Months Ended			6 Months Ended		12 Months Ended
	May. 29, 2015 USD ($)	Mar. 31, 2015 USD ($)	Feb. 28, 2015	Jan. 31, 2015	Nov. 30, 2014	Jun. 30, 2014	Nov. 30, 2013	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) MW	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
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 | 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 | 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
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, 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%
Public Utilities, ROE applicable to transmission formula rates in the MISO region, recommended by third parties			8.67%				9.15%
Public Utilities, Incremental ROE basis point increase (decrease) recommended by third parties			50
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint [Member] | Federal Energy Regulatory Commission (FERC)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Incremental ROE basis point increase (decrease) recommended 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 MISO 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 MISO region, lower bound, percentage				10.80%
Xcel Energy Inc. | 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 | 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 | 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, Increase (decrease) in transmission revenue, net of expense, due to the new ROE methodology													$ (7,000)
Maximum | NSP-Minnesota | 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, Increase (decrease) in transmission revenue, net of expense, due to the new ROE methodology													$ (9,000)