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Asset Retirement Obligation (Detail) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset retirement obligation at the beginning of period $ 2,498  
Liabilities incurred 38  
Liabilities divested (29)  
Liabilities settled (21)  
Accretion expense 73  
Revisions in estimated liabilities 66  
Liabilities held for sale (779)  
Asset retirement obligation at the end of period 1,846  
Less current portion 35 $ 66
Asset retirement obligation, long-term $ 1,811 $ 2,432