Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Funded Status of Plans at Dec. 31 [Abstract]
Noncurrent liabilities			$ (235.9)	$ (305.1)
Cash Flows [Abstract]
Total contributions to Xcel Energy's postretirement health care plans during the year			8.0	3.0	$ 10.0
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Plan amendments			1.0	0.0
Payment for Pension Benefits			47.0	63.0	61.0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets			29.3	35.5
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		$ 942.2	907.0	1,035.1
Service cost			25.4	28.0	27.8
Interest cost			37.1	35.2	40.7
Plan participants' contributions			0.0	0.0
Actuarial loss (gain)			61.7	(50.8)
Benefit payments			(90.0)	(140.5)
Obligation at Dec. 31			942.2	907.0	1,035.1
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		815.2	710.6	824.5
Actual return (loss) on plan assets			147.8	(36.5)
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant			0.0	0.0
Employer contributions			46.8	63.1
Benefit payments			(90.0)	(140.5)
Fair value of plan assets at Dec. 31			815.2	710.6	824.5
Funded Status of Plans at Dec. 31 [Abstract]
Funded status			(127.0)	(196.4)
Current liabilities			0.0	0.0
Noncurrent liabilities			(127.0)	(196.4)
Net postretirement amounts recognized on consolidated balance sheets			(127.0)	(196.4)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss			440.0	502.0
Prior service (credit) cost			(0.2)	(1.2)
Total			439.8	500.8
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Noncurrent regulatory assets			410.5	465.3
Deferred income taxes			0.0	0.0
Net-of-tax accumulated other comprehensive income			0.0	0.0
Total			$ 439.8	$ 500.8
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)			3.49%	4.31%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			$ 25.4	$ 28.0	27.8
Interest cost			37.1	35.2	40.7
Expected return on plan assets			(54.3)	(58.2)	(60.1)
Amortization of prior service cost (credit)			(0.1)	(0.1)	1.1
Amortization of net loss			30.2	38.5	39.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[1]		0.0	48.8	48.2
Net periodic postretirement benefit cost			$ 38.3	$ 92.2	$ 97.3
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)			4.31%	3.63%	4.13%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase			3.75%	3.75%	3.75%
Expected average long-term rate of return on assets (as a percent)			7.10%	7.10%	7.10%
Defined Benefit Plan Credits (Costs) Not Recognized Due To Effects of Regulation			$ (5.2)	$ (66.0)	$ (72.2)
Net benefit cost recognized for financial reporting			33.1	26.2	25.1
Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Plan amendments			0.0	0.0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets			0.0	0.0
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		75.5	76.0	88.8
Service cost			0.1	0.2	0.1
Interest cost			3.2	3.1	3.4
Plan participants' contributions			0.3	0.4
Actuarial loss (gain)			3.8	(9.0)
Benefit payments			(7.9)	(7.5)
Obligation at Dec. 31			75.5	76.0	88.8
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		2.6	2.4	6.5
Actual return (loss) on plan assets			0.0	0.0
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant			0.3	0.4
Employer contributions			7.7	3.0
Benefit payments			(7.8)	(7.5)
Fair value of plan assets at Dec. 31			2.6	2.4	6.5
Funded Status of Plans at Dec. 31 [Abstract]
Funded status			(72.9)	(73.6)
Current liabilities			(4.3)	(4.8)
Noncurrent liabilities			(68.6)	(68.8)
Net postretirement amounts recognized on consolidated balance sheets			(72.9)	(73.6)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss			36.8	34.3
Prior service (credit) cost			(9.4)	(12.4)
Total			27.4	21.9
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Noncurrent regulatory assets			25.6	20.5
Deferred income taxes			0.5	0.4
Net-of-tax accumulated other comprehensive income			1.3	1.0
Total			$ 27.4	$ 21.9
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)			3.47%	4.32%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65			6.00%	6.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65			5.10%	5.30%
Ultimate health care trend assumption rate (as a percent)			4.50%	4.50%
Period until ultimate trend rate is reached (in years)			3 years	4 years
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			$ 0.1	$ 0.2	0.1
Interest cost			3.2	3.1	3.4
Expected return on plan assets			(0.1)	(0.4)	(0.2)
Amortization of prior service cost (credit)			(3.0)	(3.0)	(3.0)
Amortization of net loss			1.5	2.4	2.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement			0.0	0.0	0.0
Net periodic postretirement benefit cost			$ 1.7	$ 2.3	$ 2.3
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)			4.32%	3.62%	4.13%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase			0.00%	0.00%	0.00%
Expected average long-term rate of return on assets (as a percent)			4.50%	5.30%	5.80%
Defined Benefit Plan Credits (Costs) Not Recognized Due To Effects of Regulation			$ 0.0	$ 0.0	$ 0.0
Net benefit cost recognized for financial reporting			1.7	2.3	2.3
Xcel Energy Inc.
Cash Flows [Abstract]
Total contributions to Xcel Energy's postretirement health care plans during the year			15.0	11.0	20.0
Xcel Energy Inc. | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits			$ 154.0	$ 150.0	$ 162.0
Subsequent Event
Cash Flows [Abstract]
Expected contribution to postretirement health care plans next year		7.0
Subsequent Event | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits		44.0
Subsequent Event | Xcel Energy Inc.
Cash Flows [Abstract]
Expected contribution to postretirement health care plans next year		10.0
Subsequent Event | Xcel Energy Inc. | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits		$ 150.0

[1] A settlement charge is required when the amount of lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In 2018 and 2017, as a result of lump-sum distributions during the 2018 and 2017 plan years, NSP-Minnesota recorded a total pension settlement charge of $48.8 million in 2018 and $48.2 million in 2017 ,