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Asset Retirement Obligations (Tables)
 6 Months Ended
Jun. 30, 2013
Asset Retirement Obligation [Abstract]  
Changes in AROs
Changes in Questar's AROs from the Condensed Consolidated Balance Sheets were as follows:
 
6 Months Ended
 
June 30,
 
2013
 
2012
 
(in millions)
AROs at beginning of year
$
67.2

 
$
63.8

Accretion
1.5

 
1.5

Liabilities incurred
1.3

 
1.7

Revisions in estimated cash flows
(6.8
)
 
(1.2
)
Liabilities settled
(0.8
)
 
(0.2
)
AROs at June 30,
$
62.4

 
$
65.6