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Benefit Plans and Other Postretirement Benefits, Pension Plan Benefit Obligations, Cash Flows and Benefit Costs (Details)
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
Plan
Dec. 31, 2018
USD ($)
Plan
Dec. 31, 2017
USD ($)
Plan
Dec. 31, 2016
USD ($)
Plan
Significant Assumptions Used to Measure Costs [Abstract]        
Expected average long-term rate of return on assets for next fiscal year (as a percent)   6.84%    
Defined Contribution Plan, Cost   $ 11.0 $ 10.0 $ 10.0
Liability, Defined Benefit Plan, Noncurrent   275.3 287.8  
Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Accumulated Benefit Obligation at Dec. 31   1,183.3 1,285.0  
Change in Projected Benefit Obligation [Roll Forward]        
Obligation at Jan. 1 $ 1,229.3 1,334.2 1,251.8  
Service cost   29.0 27.3 25.9
Interest cost   47.3 50.6 55.4
Plan amendments   0.0 (1.1)  
Actuarial (gain) loss   (96.5) 83.5  
Benefit payments   (84.7) (77.9)  
Obligation at Dec. 31   1,229.3 1,334.2 1,251.8
Change in Fair Value of Plan Assets [Roll Forward]        
Fair value of plan assets at Jan. 1 965.5 1,079.4 1,004.2  
Actual return (loss) on plan assets   (50.9) 135.6  
Employer contributions   21.7 17.5  
Plan participants' contributions   0.0 0.0  
Benefit payments   (84.7) (77.9)  
Fair value of plan assets at Dec. 31   965.5 1,079.4 1,004.2
Funded Status of Plans at Dec. 31 [Abstract]        
Funded status   263.8 254.8  
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]        
Net loss   530.8 543.7  
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax   (7.2) (10.6)  
Total   523.6 533.1  
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]        
Current regulatory assets   25.8 27.7  
Noncurrent regulatory assets   497.5 505.1  
Deferred income taxes   0.1 0.1  
Net-of-tax accumulated OCI   0.2 0.2  
Total   $ 523.6 $ 533.1  
Significant Assumptions Used to Measure Benefit Obligations [Abstract]        
Discount rate for year-end valuation (as a percent)   4.31% 3.63%  
Expected average long-term increase in compensation level (as a percent)   3.75% 3.75%  
Mortality table   RP-2014 RP-2014  
Cash Flows [Abstract]        
Total contributions to Xcel Energy's pension plans during the period   $ 22.0 $ 18.0 17.0
Components of Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost   29.0 27.3 25.9
Interest cost   47.3 50.6 55.4
Expected return on plan assets   (68.5) (68.5) (70.8)
Amortization of prior service (credit) cost   (3.4) (3.2) (3.2)
Amortization of net loss   31.2 28.3 26.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement   (4.5) 0.0 0.0
Net periodic pension cost   40.1 34.5 34.1
Defined Benefit Plan, Costs Not Recognized Due To Regulation   (3.9) (2.7) 3.4
Net benefit cost recognized for financial reporting   $ 36.2 $ 31.8 $ 37.5
Significant Assumptions Used to Measure Costs [Abstract]        
Discount rate (as a percent)   3.63% 4.13% 4.66%
Expected average long-term increase in compensation level (as a percent)   3.75% 3.75% 4.00%
Expected average long-term rate of return on assets (as a percent)   6.84% 6.84% 6.84%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant   $ 0.0 $ 0.0  
Medicare subsidy reimbursements   0.0 0.0  
Liability, Defined Benefit Plan, Noncurrent   263.8 254.8  
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position   $ (263.8) $ (254.8)  
Pension Plan [Member] | Xcel Energy Inc.        
Cash Flows [Abstract]        
Number of pension plans to which contributions were made | Plan   4 4 4
Total contributions to Xcel Energy's pension plans during the period   $ 150.0 $ 162.0 $ 125.0
Pension Plan [Member] | Subsequent Event        
Cash Flows [Abstract]        
Total contributions to Xcel Energy's pension plans during the period $ 43.0      
Significant Assumptions Used to Measure Costs [Abstract]        
Expected average long-term rate of return on assets for next fiscal year (as a percent) 6.84%      
Pension Plan [Member] | Subsequent Event | Xcel Energy Inc.        
Cash Flows [Abstract]        
Number of pension plans to which contributions were made | Plan 4      
Total contributions to Xcel Energy's pension plans during the period $ 150.0