Rate Matters, NSP-Minnesota (Details) (NSP-Minnesota, USD $)	1 Months Ended		6 Months Ended	1 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended
	Jun. 30, 2014 Electric Rate Case 2014	Oct. 31, 2013 Nuclear Project Prudency Investigation	Jun. 30, 2014 Nuclear Project Prudency Investigation	Dec. 31, 2013 Minnesota Public Utilities Commission [Member] Electric Rate Case 2014	Nov. 30, 2013 Minnesota Public Utilities Commission [Member] Electric Rate Case 2014	Jun. 30, 2014 Minnesota Public Utilities Commission [Member] Electric Rate Case 2014	Nov. 30, 2013 Minnesota Public Utilities Commission [Member] Electric Rate Case 2014, Rates 2014 [Member]	Jun. 30, 2014 Minnesota Public Utilities Commission [Member] Electric Rate Case 2014, Rates 2014 [Member]	Nov. 30, 2013 Minnesota Public Utilities Commission [Member] Electric Rate Case 2014, Rates 2015 [Member]	Jun. 30, 2014 Minnesota Public Utilities Commission [Member] Electric Rate Case 2014, Rates 2015 [Member]	Jun. 30, 2014 South Dakota Public Utilities Commission [Member] Electric Rate Case 2015 [Member]	Jun. 30, 2014 Minnesota Department of Commerce [Member] Electric Rate Case 2014	Jun. 30, 2014 Minnesota Department of Commerce [Member] Electric Rate Case 2014, Rates 2014 [Member]	Jun. 30, 2014 Minnesota Department of Commerce [Member] Electric Rate Case 2014, Rates 2015 [Member]	Jun. 30, 2014 Federal Energy Regulatory Commission (FERC) FERC Proceeding, MISO ROE Complaint [Member]	Jan. 31, 2014 Federal Energy Regulatory Commission (FERC) FERC Proceeding, MISO ROE Complaint [Member]	Nov. 30, 2013 Federal Energy Regulatory Commission (FERC) FERC Proceeding, MISO ROE Complaint [Member]	Jul. 31, 2014 Subsequent Event Nuclear Project Prudency Investigation MW	Jul. 31, 2014 Subsequent Event Minnesota Public Utilities Commission [Member] Electric Rate Case 2014	Jul. 31, 2014 Subsequent Event Minnesota Public Utilities Commission [Member] Electric Rate Case 2014, Rates 2014 [Member]		Jul. 31, 2014 Subsequent Event Minnesota Public Utilities Commission [Member] Electric Rate Case 2014, Rates 2015 [Member]	Aug. 31, 2014 Subsequent Event Minnesota Public Utilities Commission [Member] Gas Utility Infrastructure Cost Rider 2015 [Member]	Jul. 31, 2014 Subsequent Event Minnesota Department of Commerce [Member] Electric Rate Case 2014	Jul. 31, 2014 Subsequent Event Minnesota Department of Commerce [Member] Electric Rate Case 2014, Rates 2014 [Member]	Jul. 31, 2014 Subsequent Event Minnesota Department of Commerce [Member] Electric Rate Case 2014, Rates 2015 [Member]
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
Public Utilities, ROE applicable to transmission formula rates in the MISO region, upper bound																	12.38%
Public Utilities, number of years of actual results used as a baseline for a full decoupling pilot for the residential and small commercial and industrial (C&I) class													3 years
Public Utilities, number of wind projects to be excluded from requested rate increase (decrease) recommended by third parties	2
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to an increase to sales forecast																									(29,500,000)
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																									(26,900,000)
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																									(21,900,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to health care, pension and other benefits																				(800,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to property taxes																									(13,500,000)	(14,500,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to property taxes																				0		(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																										(10,800,000)
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 capital structure and disallowances																										(5,600,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to capital structure and disallowances																						0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to nuclear outage amortization																										(5,500,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to nuclear outage amortization																						0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to emission chemicals																										(3,000,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to emission chemicals																						(200,000)
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to the depreciation reserve																										22,700,000
Public Utilities, Adjustment to rate increase (decrease) recommended by public utility related to the depreciation reserve																						0
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to amortization of Prairie Island EPU costs																									(5,800,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to amortization of Prairie Island EPU costs																				(3,800,000)
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to other costs																									(2,200,000)	1,700,000
Public Utilities, Revenue deficiency based on a forecast test year																				250,000,000		68,000,000
Public Utilities, Adjustment to requested rate increase (decrease) by public utility related to the depreciation reserve																				(81,000,000)		53,000,000
Public Utilities, Adjustment to requested interim rate increase (decrease), amount																				(66,000,000)		66,000,000
Public Utilities, adjustment to requested rate increase (decrease) related to prairie island EPU																				4,000,000		(4,000,000)
Impact on revenue increase (decrease), amount																				107,000,000	[1]
Impact on revenue increase (decrease) maximum range, amount																						157,000,000
Public Utilities, Adjustment to approved rate increase (decrease) related to depreciation expense																				81,000,000		(46,000,000)
Public utilities, Adjustment to requested rate increase (decrease) related to DOE settlement proceeds, amount																				0		(26,000,000)
Public Utilities, rebuttal request to increase (decrease) 2014 rates by public utility																				169,000,000		95,000,000
Public Utilities, Recommended rate increase (decrease) impact on pre-tax income, minimum range																				188,000,000
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							193,000,000	127,000,000	98,000,000	164,000,000	15,600,000									192,700,000		98,500,000			192,700,000	98,500,000
Public Utilities, Requested Rate Increase (Decrease), Percentage							6.90%	4.60%	3.50%	5.60%	8.00%
Public Utilities, number of years excess depreciation reserve is amortized						8 years
Public Utilities, Requested Return on Equity, Percentage					10.25%						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
Public Utilities, Recommended rate increase (decrease) impact on pre-tax income, cap								208,000,000
Estimated refund obligation associated with interim rates								12,500,000
Costs for nuclear project, Amount			665,000,000															665,000,000
Total capitalized nuclear project costs			748,000,000
Initial estimated nuclear project costs			320,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				169,500,000		95,000,000
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
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%
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																									(31,300,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by public utility related to Monticello EPU costs																				0
Public Utilities, Rider costs to be recovered through base rates, amount											9,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage																				6.20%		3.50%
Public Utilities, reduction of requested rate increase (decrease), amount																						3,500,000
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to other costs																				(2,800,000)		1,000,000
Public Utilities, Rate increase (decrease) recommended by third parties													61,600,000	54,900,000										116,500,000	61,600,000	54,900,000
Public Utilities, Return on equity recommended by third parties	9.00%											9.80%
Public Utilities, Equity capital structure recommended by third parties												52.50%
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, lower bound															5,000,000
Public Utilities, reduction of transmission revenue, net of expense due to the new ROE methodology, upper bound															7,000,000
Public Utilities, Rate increase (decrease) recommended by utility																			264,500,000
Public Utilities, Recommended rate increase (decrease) impact on pre-tax income, maximum range																						$ 137,000,000

[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.