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Asset Retirement Obligation - Asset Retirement Obligation (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset retirement obligation at the beginning of period $ 2,498  
Liabilities divested (5)  
Liabilities settled (13)  
Accretion expense 36  
Asset retirement obligation at the end of period 2,516  
Less current portion 56 $ 66
Asset retirement obligation, long-term $ 2,460 $ 2,432