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Basis of Presentation - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]            
Reclassification of expense from Operating costs and expenses, Exploration expenses, and General and administrative expenses to Other, net due to adopting ASU 2017-07   $ 0   $ 9    
Cumulative effect of hedging ineffectiveness         $ 0 $ (37)
Lease, practical expedients, package     true      
Lease, practical expedient, use of hindsight     false      
Prior Period Adjustment [Abstract]            
Sales and other operating revenue $ 1,793 1,348 $ 4,673 3,803    
Marketing, including purchased oil and gas $ 491 338 $ 1,299 791    
Restatement Adjustment            
Prior Period Adjustment [Abstract]            
Sales and other operating revenue   (22)   (60)    
Marketing, including purchased oil and gas   (22)   (60)    
Scenario Previously Reported            
Prior Period Adjustment [Abstract]            
Sales and other operating revenue   1,370   3,863    
Marketing, including purchased oil and gas   $ 360   $ 851    
Retained Earnings            
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]            
Cumulative effect of hedging ineffectiveness         1 (39)
Retained Earnings | ASU 2017-12            
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]            
Cumulative effect of hedging ineffectiveness         1  
Accumulated Other Comprehensive Income (Loss)            
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]            
Cumulative effect of hedging ineffectiveness         (1) $ 0
Accumulated Other Comprehensive Income (Loss) | ASU 2017-12            
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]            
Cumulative effect of hedging ineffectiveness         $ (1)