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ASSET RETIREMENT OBLIGATIONS Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Change in Asset Retirement Obligation
The following table is a reconciliation of the carrying amount of the ARO liability for the periods presented. Changes in assumptions regarding the timing, amount, and probabilities associated with the expected cash flows, as well as the difference in actual versus estimated costs, may result in a change in the amount of the liability recognized.
 
Years Ended December 31,
 
2018
 
2017
 
2016
Beginning balance
$
57

 
$
54

 
$
58

Revisions
(33
)
 
1

 
—

Settled
(1
)
 
(1
)
 
(7
)
Accretion expense
3

 
3

 
3

Ending balance
$
26

 
$
57

 
$
54