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Accounting for Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2011
Accounting for Asset Retirement Obligations [Abstract]  
Reconciliation of Asset Retirement Obligations
  The following is a reconciliation of asset retirement obligations as of December 31, 2011 and 2010:

(Millions of Dollars)
 
2011
     
2010
 
Asset retirement liability, beginning of period
$
14.7
   
$
14.0
 
Accretion expense                                                                
 
0.6
     
0.8
 
Additional obligations                                                                
 
0.2
     
0.1
 
Reversal of obligations                                                                
 
(0.4
)
   
--
 
Payments                                                                
 
(0.2
)
   
(0.1
)
Foreign currency translation                                                                
 
(0.2
)
   
(0.1
)
Asset retirement liability, end of period                                                                
$
14.7
   
$
14.7