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Asset Retirement Obligations (Tables)
 9 Months Ended
Sep. 30, 2012
Asset Retirement Obligation [Abstract]  
Changes in AROs
Changes in Questar's AROs from the Consolidated Balance Sheets were as follows:

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

 
$
60.9

Accretion
2.3

 
2.3

Liabilities incurred
2.2

 
0.9

Revisions in estimated cash flows
(1.2
)
 
2.4

Liabilities settled
(0.8
)
 
(2.0
)
AROs at September 30,
$
66.3

 
$
64.5