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Benefit Plans and Other Postretirement Benefits, Pension Benefits (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Target Pension Asset Allocations [Abstract]        
Defined Contribution Plan, Cost   $ 12.0 $ 12.0 $ 12.0
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan        
Pension Benefits [Abstract]        
Total benefit obligation   4.0 4.0  
Net benefit cost recognized for financial reporting   1.0 1.0  
Pension Plan        
Pension Benefits [Abstract]        
Total benefit obligation   942.2 907.0 1,035.1
Net benefit cost recognized for financial reporting   $ 33.1 $ 26.2 $ 25.1
Minimum number of years historical achieved weighted average annual returns used to determine investment return assumptions (in years)   20 years    
Expected average long-term rate of return on assets (as a percent)   7.10% 7.10% 7.10%
Target Pension Asset Allocations [Abstract]        
Target pension asset allocations (as a percent)   100.00% 100.00%  
Pension Plan | Domestic and international equity securities        
Target Pension Asset Allocations [Abstract]        
Target pension asset allocations (as a percent)   37.00% 37.00%  
Pension Plan | Long-duration fixed income and interest rate swap securities        
Target Pension Asset Allocations [Abstract]        
Target pension asset allocations (as a percent)   30.00% 28.00%  
Pension Plan | Short-to-intermediate fixed income securities        
Target Pension Asset Allocations [Abstract]        
Target pension asset allocations (as a percent)   14.00% 18.00%  
Pension Plan | Alternative investments        
Target Pension Asset Allocations [Abstract]        
Target pension asset allocations (as a percent)   17.00% 15.00%  
Pension Plan | Cash        
Target Pension Asset Allocations [Abstract]        
Target pension asset allocations (as a percent)   2.00% 2.00%  
Xcel Energy Inc. | Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan        
Pension Benefits [Abstract]        
Total benefit obligation   $ 39.0 $ 33.0  
Net benefit cost recognized for financial reporting   $ 4.0    
Forecast [Member] | Pension Plan        
Pension Benefits [Abstract]        
Expected average long-term rate of return on assets for next fiscal year (as a percent) 7.10%