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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2013
Asset Retirement Obligations (Tables) [Abstract]  
Change in Asset Retirement Obligations
The following table presents the change in our AROs during 2013 and 2012:

 
2013
 
2012
 
(Millions of Dollars)
 
 
 
 
Balance as of January 1
$
44.3

 
$
55.5

Liabilities Settled
(4.4
)
 
(14.0
)
Accretion
2.4

 
2.8

Balance as of December 31
$
42.3

 
$
44.3