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Accounting for Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2018
Accounting for Asset Retirement Obligations [Abstract]  
Reconciliation of Asset Retirement Obligations
The following is a reconciliation of asset retirement obligations as of December 31, 2018 and 2017:

  
December 31,
 
(millions of dollars)
 
2018
  
2017
 
Asset retirement liability, beginning of period
 
$
22.1
  
$
21.5
 
Accretion expense
  
1.0
   
3.3
 
Other
  
2.1
   
—
 
Payments
  
(1.3
)
  
(3.2
)
Foreign currency translation
  
(0.5
)
  
0.5
 
Asset retirement liability, end of period
 
$
23.4
  
$
22.1