XML 66 R55.htm IDEA: XBRL DOCUMENT v3.10.0.1
Benefit Plans and Other Postretirement Benefits, Pension Benefits (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Pension Benefits [Abstract]      
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) 7.10% 7.10%  
Expected average long-term rate of return on assets for next fiscal year (as a percent) 7.10%    
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan      
Pension Benefits [Abstract]      
Total benefit obligation $ 1,000 $ 1,000  
Pension Plan [Member]      
Pension Benefits [Abstract]      
Total benefit obligation 156,748 157,457 $ 152,545
Net benefit cost recognized for financial reporting $ 10,571 $ 7,579 $ 8,711
Expected average long-term rate of return on assets (as a percent) 7.10% 7.10% 7.25%
Expected average long-term rate of return on assets for next fiscal year (as a percent) 7.10%    
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 100.00% 100.00%  
Pension Plan [Member] | Domestic and international equity securities      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 38.00% 40.00%  
Pension Plan [Member] | Long-duration fixed income and interest rate swap securities      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 23.00% 23.00%  
Pension Plan [Member] | Short-to-intermediate fixed income securities      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 21.00% 16.00%  
Pension Plan [Member] | Alternative investments      
Target Pension Asset Allocations [Abstract]      
Target pension asset allocations (as a percent) 16.00% 19.00%  
Pension Plan [Member] | 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 $ 37,000 $ 44,000  
Net benefit cost recognized for financial reporting $ 5,000 $ 8,000