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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, 2015
Dec. 31, 2014
Dec. 31, 2013
Change in Projected Benefit Obligation [Roll Forward]      
Obligation at Jan. 1 $ 443,753 $ 508,971  
Service cost 928 1,915 $ 2,564
Interest cost 17,498 23,704 22,210
Medicare subsidy reimbursements 1,712 1,753  
Plan participants' contributions 4,961 4,625  
Actuarial (gain) loss (32,001) (63,130)  
Benefit payments (33,277) (34,085)  
Obligation at Dec. 31 403,574 443,753 508,971
Change in Fair Value of Plan Assets [Roll Forward]      
Fair value of plan assets at Jan. 1 425,282 438,193  
Actual return (loss) on plan assets (3,076) 11,060  
Plan participants' contributions 4,961 4,625  
Employer contributions 5,552 5,489  
Benefit payments (33,277) (34,085)  
Fair value of plan assets at Dec. 31 399,442 425,282 438,193
Funded Status of Plans at Dec. 31 [Abstract]      
Funded status [1] (4,132) (18,471)  
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]      
Net loss 49,226 56,823  
Prior service (credit) cost (33,942) (40,189)  
Total 15,284 16,634  
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 $ 15,284 $ 16,634  
Significant Assumptions Used to Measure Benefit Obligations [Abstract]      
Measurement date 12/31/2015 12/31/2014  
Discount rate for year-end valuation (as a percent) 4.65% 4.08%  
Mortality table RP 2014 RP 2014  
Health care costs trend rate - initial (as a percent) 6.00% 6.50%  
Ultimate health care trend assumption rate (as a percent) 4.50% 4.50%  
Period until ultimate trend rate is reached (in years) 3 years    
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate [Abstract]      
One-percent increase in APBO $ 38,946    
One-percent decrease in APBO (33,136)    
One-percent increase in service and interest components 2,093    
One-percent decrease in service and interest components (1,743)    
Cash Flows [Abstract]      
Total contributions to Xcel Energy's postretirement health care plans during the year 5,600 $ 5,500 7,000
Expected contribution to postretirement health care plans during 2016 0    
Components of Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 928 1,915 2,564
Interest cost 17,498 23,704 22,210
Expected return on plan assets (23,803) (30,214) (29,227)
Amortization of transition obligation 0 0 785
Amortization of prior service (credit) cost (6,247) (6,247) (7,666)
Amortization of net loss 2,475 6,434 13,699
Net periodic benefit cost $ (9,149) $ (4,408) $ 2,365
Significant Assumptions Used to Measure Costs [Abstract]      
Discount rate (as a percent) 4.08% 4.82% 4.10%
Expected average long-term rate of return on assets (as a percent) 5.80% 7.18% 7.11%
Xcel Energy Inc.      
Cash Flows [Abstract]      
Total contributions to Xcel Energy's postretirement health care plans during the year $ 18,300 $ 17,100 $ 17,600
Expected contribution to postretirement health care plans during 2016 $ 12,300    
[1] Amounts are recognized in noncurrent liabilities on PSCo’s consolidated balance sheets.