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Asset Retirement Obligations (Tables)
 6 Months Ended
Jun. 30, 2012
Asset Retirement Obligation [Abstract]  
Changes in AROs
Changes in Questar's AROs from the Consolidated Balance Sheets for the six months ended June 30 were as follows:

 
6 Months Ended
 
June 30,
 
2012
 
2011
 
(in millions)
AROs at beginning of year
$
63.8

 
$
60.9

Accretion
1.5

 
1.5

Liabilities incurred
1.7

 
0.6

Revisions in estimated cash flows
(1.2
)
 
2.4

Liabilities settled
(0.2
)
 
(0.2
)
AROs at June 30,
$
65.6

 
$
65.2