Rate Matters, NSP-Minnesota (Details) (NSP-Minnesota, USD $)	1 Months Ended		9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended				9 Months Ended	1 Months Ended			9 Months Ended	1 Months Ended													9 Months Ended		1 Months Ended	9 Months Ended		1 Months Ended
	Dec. 31, 2013 MPUC Proceeding - Minnesota Electric Rate Case 2014	Nov. 30, 2013 MPUC Proceeding - Minnesota Electric Rate Case 2014	Sep. 30, 2014 MPUC Proceeding - Minnesota Electric Rate Case 2014	Oct. 31, 2013 MPUC Proceeding - Nuclear Project Prudency Investigation	Sep. 30, 2014 MPUC Proceeding - Nuclear Project Prudency Investigation	Aug. 31, 2014 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]	Jul. 31, 2014 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]		Nov. 30, 2013 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]	Sep. 30, 2014 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]	Aug. 31, 2014 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]	Jul. 31, 2014 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]	Nov. 30, 2013 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]	Sep. 30, 2014 MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]	Jan. 31, 2014 FERC Proceeding, MISO ROE Complaint [Member]	Nov. 30, 2013 FERC Proceeding, MISO ROE Complaint [Member]	Aug. 31, 2014 MPUC Proceeding - Minnesota Gas Utility Infrastructure Cost Rider 2015 [Member]	Jun. 30, 2014 SDPUC Proceeding - South Dakota Electric Rate Case 2015	Dec. 31, 2013 Minnesota Public Utilities Commission [Member] MPUC Proceeding - Minnesota Electric Rate Case 2014	Aug. 31, 2014 Minnesota Department of Commerce [Member] MPUC Proceeding - Minnesota Electric Rate Case 2014	Jul. 31, 2014 Minnesota Department of Commerce [Member] MPUC Proceeding - Nuclear Project Prudency Investigation MW	Aug. 31, 2014 Minnesota Department of Commerce [Member] MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]	Jul. 31, 2014 Minnesota Department of Commerce [Member] MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2014 [Member]	Aug. 31, 2014 Minnesota Department of Commerce [Member] MPUC Proceeding - Minnesota Electric Rate Case 2014, Rates 2015 [Member]	Jun. 30, 2014 Federal Energy Regulatory Commission (FERC) FERC Proceeding, MISO ROE Complaint [Member]	Aug. 31, 2014 Office of Attorney General (OAG) [Member] MPUC Proceeding - Nuclear Project Prudency Investigation	Oct. 31, 2014 Subsequent Event Minnesota Department of Commerce [Member] MPUC Proceeding - Minnesota Gas Utility Infrastructure Cost Rider 2015 [Member]	Sep. 30, 2014 Minimum MPUC Proceeding - Nuclear Project Prudency Investigation MW	Sep. 30, 2014 Minimum FERC Proceeding, MISO ROE Complaint [Member]	Aug. 31, 2014 Minimum Minnesota Department of Commerce [Member] MPUC Proceeding - Minnesota Electric Rate Case 2014	Sep. 30, 2014 Maximum MPUC Proceeding - Nuclear Project Prudency Investigation MW	Sep. 30, 2014 Maximum FERC Proceeding, MISO ROE Complaint [Member]	Aug. 31, 2014 Maximum Minnesota Department of Commerce [Member] MPUC Proceeding - Minnesota Electric Rate Case 2014
Public Utilities, General Disclosures [Line Items]
Public Utilities, number of years rate case is applicable for		2 years
Public Utility, Deferred sewer separation costs																	$ 4,800,000
Number of years cost deferral is amortized																											five
Public Utilities, ROE applicable to transmission formula rates in the MISO region, upper bound																12.38%
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to an increase to sales forecast																						(43,200,000)
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to an increase to sales forecast						(15,800,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to a lower return on equity																						(36,200,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to a lower return on equity						0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to health care, pension and other benefits																						(11,400,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to health care, pension and other benefits						(1,900,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to property taxes																				(9,000,000)		(9,000,000)		(3,300,000)
Property tax forecast																														141,000,000			145,000,000
Amount of public utility's amended requested rate increase (decrease) with regulatory agency, unadjusted.						142,200,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility, property taxes true up.						3,900,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to property taxes						(9,000,000)					(3,300,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to PTCs moving to base rates																								(11,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to PTCs moving to base rates											(11,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to DOE settlement proceeds																								10,100,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to DOE settlement proceeds											10,100,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to emission chemicals																								(1,600,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to emission chemicals											(1,600,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to amortization of Prairie Island EPU costs																						(5,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to amortization of Prairie Island EPU costs						(5,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to other costs																						(8,000,000)		(4,800,000)
Public Utilities, Revenue deficiency based on a forecast test year							250,600,000					67,800,000
Public Utilities, Adjustment to requested rate increase (decrease) by public utility related to the evidentiary hearing adjustments							(27,300,000)					11,000,000
Public Utilities, Amended revenue deficiency based on a forecast test year							223,300,000					78,800,000
Public Utilities, Adjustment to requested rate increase (decrease) by public utility related to the depreciation reserve							(81,100,000)					52,900,000
Public Utilities, Adjustment to requested interim rate increase (decrease), amount							(65,300,000)					65,300,000
Public Utilities, adjustment to requested rate increase (decrease) related to prairie island EPU							4,800,000					(4,800,000)
Impact on revenue increase (decrease), amount							81,700,000	[1]
Impact on revenue increase (decrease) maximum range, amount												166,500,000
Public Utilities, Adjustment to approved rate increase (decrease) related to depreciation expense							81,100,000					(45,700,000)
Public utilities, Adjustment to requested rate increase (decrease) related to DOE settlement proceeds, amount							0					(25,700,000)
Public Utilities, rebuttal request to increase (decrease) 2014 rates by public utility							142,200,000					106,000,000
Public Utilities, Recommended rate increase (decrease) impact on pre-tax income, minimum range							153,700,000
Public Utilities, adjustment requested by public utility related to nuclear investments and operating costs																		13,400,000
Public Utilities, adjustment requested by public utility related to other production, transmission and distribution costs																		5,000,000
Public Utilities, adjustment to requested rate increase (decrease) requested by public utility related to technology improvements																		2,100,000
Public Utilities, adjustment to requested rate increase (decrease) requested by public utility related to pension and operating and maintenance expenses																		1,600,000
Public Utilities, adjustment to requested rate increase (decrease) requested by public utility related to wind generation facilities																		1,400,000
Public Utilities, adjustment to requested rate increase (decrease) requested by public utility related to capital structure																		1,100,000
Public Utilities, Incremental base revenue requested																		24,600,000
Public Utilities, adjustment to requested rate increase (decrease) requested by public utility related to infrastructure rider recovery moving to base rates																		(8,400,000)
Public Utilities, adjustment to requested rate increase (decrease) requested by public utility related to TCR rider recovery moving to base rates																		(600,000)
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount						192,700,000			193,000,000		98,500,000		98,000,000					15,600,000				192,700,000		98,500,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									6.90%				3.50%					8.00%
Public Utilities, number of years excess depreciation reserve is amortized			8 years																			3 years
Public Utilities, Requested Return on Equity, Percentage		10.25%																10.25%
Public Utilities, Requested Rate Base, Amount									6,670,000,000				412,000,000					433,200,000
Public Utilities, Requested Equity Capital Structure, Percentage		52.50%																53.86%
Public Utilities, Interim Rate Increase (Decrease), Amount	127,000,000									127,000,000									127,000,000
Public Utilities, Interim Rate Increase (Decrease), Percentage										4.60%
Public Utilities, Recommended rate increase (decrease) impact on pre-tax income, cap										208,000,000
Generating capacity																												600			671
Costs for nuclear project, Amount					665,000,000																665,000,000
Total capitalized nuclear project costs					748,000,000																					748,000,000
Amount of recoverable investment, without a return																										107,000,000
Cost per kilowatt of installed capacity					1,000
Initial estimated nuclear project costs					320,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											106,000,000			164,000,000
Public Utilities, Estimated adjusted cumulative total step increase (decrease) recommended by third parties.																								134,600,000
Public Utilities, Unadjusted cumulative total step increase (decrease) recommended by third parties.																								112,400,000
Amount of public utility's amended unadjusted cumulative total step up increase (decrease) with regulatory agency.											248,200,000
Number of factors attributable to project cost increases				3
Public Utilities, minimum number of years for the application process				5
Public Utilities, Total cost disallowances recommended by third parties																					71,500,000					321,000,000
Public Utilities, disallowance of project costs recommended by third parties impacting the NSP System																					94,000,000
Number of megawatts of additional capacity																					71
Percentage of total project costs associated with project components required to achieve the EPU					85.00%																85.00%
Number of sales forecast methodologies																							2
Number of months of actual weather normalized sales, true up adjustment																				12 months
Public Utilities, Requested increase (decrease) to rider revenue																	14,900,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to depreciation expense																								(17,500,000)
Public Utilities, Adjustment to requested rate increase (decrease) by public utility related to depreciation expense											0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to Monticello EPU costs																						(33,900,000)		29,100,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to excess depreciation reserve adjustment.																								(22,700,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to excess depreciation reserve adjustment.											0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU costs						0					0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to Monticello EPU cost disallowance.																								(10,200,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU cost disallowance.											0
Public Utilities, Rider costs to be recovered through base rates, Amount																		9,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage							5.10%					3.80%		5.60%
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to other costs						(6,500,000)					1,700,000
Amount of the rate increase (decrease) recommended by third parties, unadjusted.																						45,900,000
Public Utilities, Rate increase (decrease) recommended by third parties																								66,500,000
Public Utilities, ROE applicable to transmission formula rates in the MISO region, lower bound															9.15%	9.15%
Public Utilities, maximum equity capital structure percentage allowed per the complaint																50.00%
Public Utilities, number of steps required for newly adopted ROE discounted cash flow methodology																									2
Public Utilities, reduction of transmission revenue, net of expense due to the new ROE methodology																													5,000,000			7,000,000
Public Utilities, Recommended rate increase (decrease) impact on pre-tax income, maximum range												146,500,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to Monticello EPU depreciation deferrals																						0		0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU depreciation deferrals						(12,200,000)					1,600,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to Monticello EPU step increase.																								0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU step increase.											10,100,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties, sales forecast true up.																						18,300,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by Public Utility, sales forecast true up.						(9,100,000)	(9,100,000)	[2]				0											(9,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third party, property taxes true up.																						3,900,000
Amount of the rate increase (decrease) recommended by third parties, adjusted.																						68,100,000
Amount of public utility's amended requested rate increase (decrease) with regulatory agency, adjusted.						137,000,000
Amount of public utility's amended estimated adjusted cumulative total step up increase (decrease) with regulatory agency.											$ 243,000,000

[1] NSP-Minnesota’s total revenue for 2014 is capped at the interim rate level of $127 million and pre-tax operating income is capped at $208 million. This table demonstrates the impact of reducing NSP-Minnesota’s rebuttal request.

[2] NSP-Minnesota and the DOC have agreed to a sales true-up based on weather normalized sales for 2014, using standard weather coefficients. NSP-Minnesota periodically adjusts the coefficients in periods of extreme weather conditions to enhance weather impact estimates. As a result of the difference in the two methodologies, currently, approximately $9.1 million of revenue that NSP-Minnesota attributed to weather would be considered normal sales growth using the standard weather coefficients. The refund for the full year could vary from the estimate as of Sept. 30, 2014, depending on weather conditions.