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Share-Based Compensation Performance shares (Details) (Performance Shares [Member], USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Major assumptions used in the calculation of fair value of performance shares granted [Abstract]      
Weighted-average grant date fair value, performance shares granted (in dollars per share) $ 39.62 $ 25.42 $ 18.23
Risk-free interest rate (in hundredths) 0.40% 0.35% 1.32%
Expected price volatility (in hundredths) 19.00% 22.00% 31.30%
Expected dividend yield (in hundredths) 2.88% 3.35% 3.39%
Expected life (in years and months) 2 years 11 months 2 years 11 months 2 years 11 months
Transactions under the terms of the LTSIP - shares [Roll Forward]      
Balance at December 31, 2012 264,867    
Granted 126,606    
Forfeited (3,594)    
Balance at December 31, 2013 387,879 264,867  
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2012 $ 21.94    
Granted $ 39.62 $ 25.42 $ 18.23
Forfeited $ 33.09    
Balance at December 31, 2013 $ 27.61 $ 21.94  
Performance shares, additional disclosures [Abstract]      
Performance period that the target number of performance shares for each exectutive officer is subject to adjustment based on the company's performance (in years) 3 years    
Equity- and liability-based performance share compensation expense $ 2.0 $ 1.8 $ 0.6
Weighted-average remaining vesting period of share-based awards issued (in months) 18 months    
Vested Undistributed [Member]
     
Transactions under the terms of the LTSIP - shares [Roll Forward]      
Balance at December 31, 2013 130,221    
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2013 $ 18.44    
Performance shares, additional disclosures [Abstract]      
The date the share-based award will be distributed first quarter of 2014    
Minimum [Member]
     
Major assumptions used in the calculation of fair value of performance shares granted [Abstract]      
Weighted-average grant date fair value, performance shares granted (in dollars per share) $ 39.62    
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2012 $ 18.23    
Granted $ 39.62    
Forfeited $ 18.23    
Balance at December 31, 2013 $ 18.23    
Maximum [Member]
     
Major assumptions used in the calculation of fair value of performance shares granted [Abstract]      
Weighted-average grant date fair value, performance shares granted (in dollars per share) $ 39.62    
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2012 $ 25.42    
Granted $ 39.62    
Forfeited $ 39.62    
Balance at December 31, 2013 $ 39.62    
Questar Gas [Member]
     
Transactions under the terms of the LTSIP - shares [Roll Forward]      
Balance at December 31, 2013 34,326    
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2013 $ 27.91    
Performance shares, additional disclosures [Abstract]      
Weighted-average remaining vesting period of share-based awards issued (in months) 18 months    
Questar Gas [Member] | Minimum [Member]
     
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2013 $ 18.23    
Questar Gas [Member] | Maximum [Member]
     
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2013 $ 39.62    
Questar Pipeline [Member]
     
Transactions under the terms of the LTSIP - shares [Roll Forward]      
Balance at December 31, 2013 65,283    
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2013 $ 26.85    
Performance shares, additional disclosures [Abstract]      
Weighted-average remaining vesting period of share-based awards issued (in months) 18 months    
Questar Pipeline [Member] | Minimum [Member]
     
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2013 $ 18.23    
Questar Pipeline [Member] | Maximum [Member]
     
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]      
Balance at December 31, 2013 $ 39.62