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Asset Retirement Obligations (Tables)
 6 Months Ended
Jun. 30, 2016
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,
 
2016
 
2015
 
(in millions)
AROs at beginning of year
$
67.6

 
$
69.3

Accretion
2.1

 
1.7

Liabilities incurred
0.2

 
0.5

Revisions in estimated cash flows
2.1

 
5.7

Liabilities settled
(0.6
)
 
(6.6
)
AROs at end of period
$
71.4

 
$
70.6