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Accounting for Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2012
Accounting for Asset Retirement Obligations [Abstract]  
Reconciliation of Asset Retirement Obligations
     The following is a reconciliation of asset retirement obligations as of December 31, 2012 and 2011:

(Millions of Dollars)
 
2012
 
 
 
2011
 
Asset retirement liability, beginning of period
$
14.7
 
 
$
14.7
 
Accretion expense                                                                                    
 
0.7
 
 
 
0.6
 
Additional obligations                                                                                    
 
0.1
 
 
 
0.2
 
Reversal of obligations                                                                                    
 
(0.2
)
 
 
(0.4
)
Payments                                                                                    
 
(0.3
)
 
 
(0.2
)
Foreign currency translation                                                                                    
 
--
 
 
 
(0.2
)
Asset retirement liability, end of period                                                                                    
$
15.0
 
 
$
14.7