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Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - Postretirement Benefit Plan - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Change in Projected Benefit Obligation [Roll Forward]      
Obligation at Jan. 1 $ 403,574 $ 443,753  
Service cost 768 928 $ 1,915
Interest cost 18,070 17,498 23,704
Medicare subsidy reimbursements 1,901 1,712  
Plan participants' contributions 5,376 4,961  
Actuarial (gain) loss 27,355 (32,001)  
Benefit payments (35,221) (33,277)  
Obligation at Dec. 31 421,823 403,574 443,753
Change in Fair Value of Plan Assets [Roll Forward]      
Fair value of plan assets at Jan. 1 399,442 425,282  
Actual return (loss) on plan assets 18,590 (3,076)  
Plan participants' contributions 5,376 4,961  
Employer contributions 5,368 5,552  
Benefit payments (35,221) (33,277)  
Fair value of plan assets at Dec. 31 393,555 399,442 425,282
Funded Status of Plans at Dec. 31 [Abstract]      
Funded status [1] (28,268) (4,132)  
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]      
Net loss 78,359 49,226  
Prior service (credit) cost (27,695) (33,942)  
Total 50,664 15,284  
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]      
Noncurrent regulatory assets $ 50,664 $ 15,284  
Significant Assumptions Used to Measure Benefit Obligations [Abstract]      
Discount rate for year-end valuation (as a percent) 4.13% 4.65%  
Mortality table RP 2014 RP 2014  
Health care costs trend rate - initial (as a percent) 5.50% 6.00%  
Ultimate health care trend assumption rate (as a percent) 4.50% 4.50%  
Period until ultimate trend rate is reached (in years) 2 years    
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate [Abstract]      
One-percent increase in APBO $ 40,100    
One-percent decrease in APBO (34,155)    
One-percent increase in service and interest components 1,980    
One-percent decrease in service and interest components (1,677)    
Cash Flows [Abstract]      
Total contributions to Xcel Energy's postretirement health care plans during the year 5,400 $ 5,600 5,500
Expected contribution to postretirement health care plans during 2017 0    
Components of Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 768 928 1,915
Interest cost 18,070 17,498 23,704
Expected return on plan assets (22,299) (23,803) (30,214)
Amortization of prior service (credit) cost (6,247) (6,247) (6,247)
Amortization of net loss 1,931 2,475 6,434
Net periodic pension cost $ (7,777) $ (9,149) $ (4,408)
Significant Assumptions Used to Measure Costs [Abstract]      
Discount rate (as a percent) 4.65% 4.08% 4.82%
Expected average long-term rate of return on assets (as a percent) 5.80% 5.80% 7.18%
Xcel Energy Inc.      
Cash Flows [Abstract]      
Total contributions to Xcel Energy's postretirement health care plans during the year $ 17,900 $ 18,300 $ 17,100
Expected contribution to postretirement health care plans during 2017 $ 11,800    
[1] Amounts are recognized in noncurrent liabilities on PSCo’s consolidated balance sheets.