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Accounting for Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2014
Accounting for Asset Retirement Obligations [Abstract]  
Reconciliation of asset retirement obligations
The following is a reconciliation of asset retirement obligations as of December 31, 2014 and 2013:

  
2014
  
2013
 
  
(millions of dollars)
 
Asset retirement liability, beginning of period
 
$
14.7
  
$
15.0
 
Acquisition
  
9.2
   
-
 
Accretion expense
  
1.7
   
0.9
 
Reversals
  
(0.2
)
  
(0.4
)
Payments
  
(1.5
)
  
(0.6
)
Foreign currency translation
  
(0.9
)
  
(0.2
)
Asset retirement liability, end of period
 
$
23.0
  
$
14.7