Annual report pursuant to Section 13 and 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ASSET RETIREMENT OBLIGATIONS (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ASSET RETIREMENT OBLIGATIONS (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
ASSET RETIREMENT OBLIGATIONS    
Asset retirement obligations $ 9 $ 8