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Asset Retirement Obligation - Asset Retirement Obligation (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Asset Retirement Obligation Disclosure [Abstract]      
Asset retirement obligation at beginning of year $ 4,578 $ 3,887  
Liabilities incurred 481 592  
Liabilities acquired 53 72  
Liabilities divested (1,692)    
Liabilities settled (497) (550)  
Accretion expense 238 228 150
Revisions in estimated liabilities 56 345  
Asset retirement obligation at end of year 3,222 4,578 3,887
Less current portion (121) (478)  
Asset retirement obligation, long-term $ 3,101 $ 4,100