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Accounting for Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2020
Accounting for Asset Retirement Obligations [Abstract]  
Reconciliation of Asset Retirement Obligations

The following is a reconciliation of asset retirement obligations as of December 31, 2020 and 2019:

  
December 31,
  
(millions of dollars)
  
2020
    
2019
  
Asset retirement obligation, beginning of period
  
$
23.9
    
$
23.4
  
Accretion expense
    
2.3
      
2.7
  
Other
    
1.1
      
1.1
  
Payments
    
(3.4
)
    
(3.3
)
Foreign currency translation
    
0.2
      
—
  
Asset retirement obligation, end of period
  
$
24.1
    
$
23.9