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Benefit Plans and Other Postretirement Benefits, Pension Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - Pension Plans
$ in Thousands
1 Months Ended 12 Months Ended
Jan. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Plan
Dec. 31, 2015
USD ($)
Plan
Dec. 31, 2014
USD ($)
Plan
Defined Benefit Plan Disclosure [Line Items]        
Accumulated Benefit Obligation at Dec. 31   $ 1,213,890 $ 1,192,798  
Change in Projected Benefit Obligation [Roll Forward]        
Obligation at Jan. 1 $ 1,251,822 1,224,650 1,277,957  
Service cost   25,926 28,260 $ 23,939
Interest cost   55,405 50,857 53,277
Transfer (to) from other plan   (9,149) (2,938)  
Plan amendments   206 0  
Actuarial (gain) loss   51,779 (54,737)  
Benefit payments   (96,995) (74,749)  
Obligation at Dec. 31   1,251,822 1,224,650 1,277,957
Change in Fair Value of Plan Assets [Roll Forward]        
Fair value of plan assets at Jan. 1 1,004,213 1,036,681 1,103,865  
Actual return (loss) on plan assets   56,762 (9,122)  
Employer contributions   16,829 20,056  
Transfer (to) from other plan   (9,064) (3,369)  
Benefit payments   (96,995) (74,749)  
Fair value of plan assets at Dec. 31   1,004,213 1,036,681 1,103,865
Funded Status of Plans at Dec. 31 [Abstract]        
Funded status [1]   (247,609) (187,969)  
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]        
Net loss   554,999 521,703  
Prior service (credit) cost   (12,155) (15,572)  
Total   542,844 506,131  
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]        
Current regulatory assets   515,708 28,852  
Noncurrent regulatory assets   26,853 477,279  
Deferred income taxes   108 0  
Net-of-tax accumulated OCI   175 0  
Total   $ 542,844 $ 506,131  
Significant Assumptions Used to Measure Benefit Obligations [Abstract]        
Discount rate for year-end valuation (as a percent)   4.13% 4.66%  
Expected average long-term increase in compensation level (as a percent)   3.75% 4.00%  
Mortality table   RP-2014 RP-2014  
Cash Flows [Abstract]        
Total contributions to Xcel Energy's pension plans during the period   $ 16,800 $ 20,100 35,200
Components of Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost   25,926 28,260 23,939
Interest cost   55,405 50,857 53,277
Expected return on plan assets   (70,769) (72,590) (70,709)
Amortization of prior service (credit) cost   (3,211) (3,136) (3,092)
Amortization of net loss   26,771 36,377 33,892
Net periodic pension cost   34,122 39,768 37,307
Costs not recognized due to regulation   3,364 (1,464) 0
Net benefit cost recognized for financial reporting   $ 37,486 $ 38,304 $ 37,307
Significant Assumptions Used to Measure Costs [Abstract]        
Discount rate (as a percent)   4.66% 4.11% 4.75%
Expected average long-term increase in compensation level (as a percent)   4.00% 3.75% 3.75%
Expected average long-term rate of return on assets (as a percent)   6.84% 6.81% 6.81%
Allocated costs for pension plans sponsored by Xcel Energy Inc.   $ 9,400 $ 9,900 $ 9,400
Expected average long-term rate of return on assets for next fiscal year (as a percent)   6.62%    
Number of years fair market value of plan assets is adjusted using calculated value method (in years)   5 years    
Annual adjustment rate used in calculated value method (as a percent)   20.00%    
Xcel Energy Inc.        
Cash Flows [Abstract]        
Number of pension plans to which contributions were made | Plan   4 4 4
Total contributions to Xcel Energy's pension plans during the period   $ 125,200 $ 90,100 $ 130,600
Subsequent Event        
Cash Flows [Abstract]        
Total contributions to Xcel Energy's pension plans during the period 16,800      
Subsequent Event | Xcel Energy Inc.        
Cash Flows [Abstract]        
Total contributions to Xcel Energy's pension plans during the period $ 150,000      
[1] Amounts are recognized in noncurrent liabilities on PSCo’s consolidated balance sheets.