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Asset Retirement Obligations (Tables)
 3 Months Ended
Mar. 31, 2016
Asset Retirement Obligation [Abstract]  
Changes in AROs
Changes in Questar's AROs from the Condensed Consolidated Balance Sheets were as follows:
 
3 Months Ended
 
March 31,
 
2016
 
2015
 
(in millions)
AROs at beginning of year
$
67.6

 
$
69.3

Accretion
1.0

 
0.8

Liabilities incurred
0.2

 
0.1

Revisions in estimated cash flows
2.1

 
5.7

Liabilities settled
(0.4
)
 
(0.9
)
AROs at end of period
$
70.5

 
$
75.0