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Accounting for Asset Retirement Obligations (Tables)
 6 Months Ended
Jun. 30, 2019
Accounting for Asset Retirement Obligations [Abstract]  
Reconciliation of Asset Retirement Obligations The following is a reconciliation of asset retirement obligations as of June 30, 2019:

(millions of dollars)
      
Asset retirement liability, December 31, 2018
  
$
23.4
  
Accretion expense
    
1.4
  
Other
    
0.5
  
Payments
    
(1.5
)
Foreign currency translation
    
(0.1
)
Asset retirement liability, June 30, 2019
  
$
23.7