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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ASSET RETIREMENT OBLIGATIONS (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Accounting Policies [Abstract]    
Asset retirement obligation, included in deferred credits and other liabilities-other $ 1,424 $ 1,241
Asset retirement obligation    
Beginning balance 1,312 1,369
Liabilities incurred – capitalized to PP&E 31 46
Liabilities settled and paid (40) (39)
Accretion expense 67 67
Acquisitions, dispositions and other – changes in PP&E (18) (136)
Revisions to estimated cash flows – changes in PP&E 147 5
Ending balance $ 1,499 $ 1,312