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ASSET RETIREMENT OBLIGATIONS (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Changes in ARO liability      
Asset retirement obligations, beginning of period $ 136 $ 21 $ 17
Additional liabilities incurred 8 3 2
Liabilities acquired 4 111 2
Liabilities settled (61) (2) (1)
Accretion expense 7 2 1
Revisions in estimated liabilities 0 1 0
Asset retirement obligations, end of period 94 136 21
Less current portion 0 0 1
Asset retirement obligations - long-term $ 94 $ 136 $ 20