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ASSET RETIREMENT OBLIGATIONS (Tables)
 12 Months Ended
Dec. 31, 2017
Asset Retirement Obligation [Abstract]  
Carrying value of asset retirement obligations
The changes in the carrying amount of the Company’s asset retirement obligations were as follows:
 
2017
 
2016
Beginning balance as of January 1,
$
965.5

 
$
856.9

Additions
33.4

 
64.1

Accretion expense
94.5

 
67.0

Revisions in estimates (1)
86.6

 
(21.1
)
Settlements
(4.7
)
 
(1.4
)
Balance as of December 31,
$
1,175.3

 
$
965.5

 
_______________
(1)
Revisions in estimates include an increase to the liability of $13.0 million and $9.6 million related to foreign currency translation for the years ended December 31, 2017 and 2016, respectively