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Benefit Plans and Other Postretirement Benefits, Pension Benefits (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan      
Pension Benefits [Abstract]      
Total benefit obligation $ 3,600 $ 3,800  
Net benefit cost recognized for financial reporting 600 600  
Pension Plans      
Pension Benefits [Abstract]      
Total benefit obligation 1,224,650 1,277,957 $ 1,152,836
Net benefit cost recognized for financial reporting $ 38,304 $ 37,307 $ 49,899
Minimum number of years historical achieved weighted average annual returns are used to determine investment return assumptions (in years) 20 years    
Expected average long-term rate of return on assets (as a percent) 6.81% 6.81% 6.47%
Expected average long-term rate of return on assets for next fiscal year (as a percent) 6.84%    
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 100.00% 100.00%  
Pension Plans | Domestic and international equity securities      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 36.00% 32.00%  
Pension Plans | Long-duration fixed income and interest rate swap securities      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 32.00% 35.00%  
Pension Plans | Short-to-intermediate fixed income securities      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 12.00% 12.00%  
Pension Plans | Alternative investments      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 18.00% 18.00%  
Pension Plans | Cash      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 2.00% 3.00%  
Xcel Energy Inc. | Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan      
Pension Benefits [Abstract]      
Total benefit obligation $ 41,800 $ 46,500  
Net benefit cost recognized for financial reporting $ 9,500 $ 4,700