Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Payment for Settlement		$ 6.8	$ 6.9
Significant Assumptions Used to Measure Costs [Abstract]
Liability, Defined Benefit Plan, Noncurrent		(67.0)	(92.4)
Operating and maintenance expenses		285.3	282.7	$ 285.4
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan amendments		0.0	0.0
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1	$ 43.2	41.8	47.0
Service cost		0.9	1.1	0.9
Interest cost		1.7	1.6	1.7
Plan participant's contributions		0.6	0.6
Actuarial loss		0.4	(5.1)
Benefit payments		(2.2)	(3.4)
Obligation at Dec. 31		43.2	41.8	47.0
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	43.6	40.0	44.1
Actual return on plan assets		5.1	(1.3)
Plan participant's contributions		0.6	0.6
Employer contributions		0.1	0.0
Benefit payments		(2.2)	(3.4)
Fair value of plan assets at Dec. 31		43.6	40.0	44.1
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		0.4	(1.8)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		(11.9)	(9.6)
Prior service credit		(1.4)	(1.8)
Total		(13.3)	(11.4)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost (Credit) Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		0.0	0.0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		0.0	0.0
Current regulatory liabilities		(0.8)	(0.9)
Noncurrent regulatory liabilities		(12.5)	(10.5)
Total		$ (13.3)	$ (11.4)
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		3.47%	4.32%
Mortality table		Pri-2012	RP-2014
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		$ 0.9	$ 1.1	0.9
Interest cost		1.7	1.6	1.7
Expected return on plan assets		(2.0)	(2.5)	(2.4)
Amortization of prior service cost		(0.5)	(0.4)	(0.4)
Amortization of net loss		(0.4)	(0.4)	(0.6)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		0.0	0.0	0.0
Net periodic pension cost		$ (0.3)	$ (0.6)	$ (0.8)
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)		4.32%	3.62%	4.13%
Expected average long-term increase in compensation level (as a percent)		0.00%	0.00%	0.00%
Expected average long-term rate of return on assets (as a percent)		5.30%	5.80%	5.80%
Liability, Defined Benefit Plan, Noncurrent		$ 0.0	$ (1.8)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		0.4	(1.8)
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0.0	0.0	$ 0.0
Net benefit cost recognized for financial reporting		(0.3)	(0.6)	(0.8)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Payment for Settlement		2.4	3.2
Payment for Pension Benefits		18.0	8.0	24.0
Plan amendments		0.0	0.0
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1	518.8	477.8	515.9
Service cost		8.8	9.7	9.8
Interest cost		20.1	18.4	19.7
Plan participant's contributions		0.0	0.0
Actuarial loss		44.2	(34.8)
Benefit payments		(32.1)	(31.4)
Obligation at Dec. 31		518.8	477.8	515.9
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	458.2	392.2	433.2
Actual return on plan assets		80.2	(17.6)
Plan participant's contributions		0.0	0.0
Employer contributions		17.9	8.0
Benefit payments		(32.1)	(31.4)
Fair value of plan assets at Dec. 31		458.2	392.2	433.2
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		(60.6)	(85.6)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		209.7	230.9
Prior service credit		(1.1)	(1.2)
Total		208.6	229.7
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost (Credit) Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		11.0	12.9
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		197.6	216.8
Current regulatory liabilities		0.0	0.0
Noncurrent regulatory liabilities		0.0	0.0
Total		$ 208.6	$ 229.7
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		3.49%	4.31%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.75%	3.75%
Mortality table		Pri-2012	RP-2014
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 8.8	$ 9.7	9.8
Interest cost		20.1	18.4	19.7
Expected return on plan assets		(28.6)	(28.3)	(27.9)
Amortization of prior service cost		(0.1)	(0.1)	0.0
Amortization of net loss		11.3	14.1	13.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		(2.4)	(3.2)	0.0
Net periodic pension cost		$ 13.9	$ 17.0	$ 14.6
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)		4.31%	3.63%	4.13%
Expected average long-term increase in compensation level (as a percent)		3.75%	3.75%	3.75%
Expected average long-term rate of return on assets (as a percent)		6.78%	6.78%	6.78%
Liability, Defined Benefit Plan, Noncurrent		$ (60.6)	$ (85.6)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		(60.6)	(85.6)
Defined Benefit Plan, Costs Not Recognized Due To Regulation		(0.9)	2.2	$ (0.3)
Net benefit cost recognized for financial reporting		14.8	14.8	14.9
Operating and maintenance expenses		0.6	0.7
Parent Company [Member]
Cash Flows [Abstract]
Total contributions to Xcel Energy's postretirement health care plans during the year		15.0	11.0	20.0
Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits		$ 154.0	$ 150.0	$ 162.0
Subsequent Event | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits	14.0
Subsequent Event | Parent Company [Member]
Cash Flows [Abstract]
Expected contribution to postretirement health care plans during 2019					$ 10.0
Subsequent Event | Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits	$ 150.0