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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ASSET RETIREMENT OBLIGATIONS (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
ASSET RETIREMENT OBLIGATIONS    
Asset retirement obligation, included in deferred credits and other liabilities-other $ 1,200 $ 1,200
Asset retirement obligation    
Beginning balance 1,124 1,091
Liabilities incurred - capitalized to PP&E 46 46
Liabilities settled and paid (38) (35)
Accretion expense 59 54
Acquisitions, dispositions and other - changes in PP&E 11 (209)
Revisions to estimated cash flows - changes in PP&E 167 177
Ending balance $ 1,369 $ 1,124