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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ASSET RETIREMENT OBLIGATIONS (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Asset retirement obligation    
Asset retirement obligation, included in deferred credits and other liabilities-other $ 1,241 $ 1,245
Beginning balance 1,369 1,124
Liabilities incurred - capitalized to PP&E 46 46
Liabilities settled and paid (39) (38)
Accretion expense 67 59
Acquisitions, dispositions and other - changes in PP&E (136) 11
Revisions to estimated cash flows - changes in PP&E 5 167
Ending balance $ 1,312 $ 1,369