|**Capitalized Exploratory Well Costs (Tables)**                                                                                             | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|**Capitalized Exploratory Well Costs [Abstract]**                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Changes in Capitalized Exploratory Well Costs                                                                                               | Changes in capitalized exploratory well costs are as follows and exclude amounts that were capitalized and subsequently expensed in the same period:Nine Months Ended September 30, 2013(millions)Capitalized Exploratory Well Costs, Beginning of Period$900Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves586Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves(34)Capitalized Exploratory Well Costs Charged to Expense(3)Capitalized Exploratory Well Costs, End of Period$1,449                                                                 
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|                                                                                                                                            | Nine Months Ended September 30, 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(millions)                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Capitalized Exploratory Well Costs, Beginning of Period                                                                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves                                                    | 586                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves                                                     | (34                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Capitalized Exploratory Well Costs Charged to Expense                                                                                       | (3                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Capitalized Exploratory Well Costs, End of Period                                                                                           | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Aging of Capitalized Well Costs                                                                                                             | The following table provides an aging of capitalized exploratory well costs based on the date that drilling commenced, and the number of projects that have been capitalized for a period greater than one year:September 30, 2013December 31, 2012(millions)Exploratory Well Costs Capitalized for a Period of One Year or Less$732$355Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling717545Balance at End of Period$1,449$900Number of Projects with Exploratory Well Costs That Have Been Capitalized for a Period Greater Than One Year Since Commencement of Drilling1314
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|                                                                                                                                            | September 30, 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|(millions)                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Exploratory Well Costs Capitalized for a Period of One Year or Less                                                                         | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                        | 717                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Balance at End of Period                                                                                                                    | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Number of Projects with Exploratory Well Costs That Have Been Capitalized for a Period Greater Than One Year Since Commencement of Drilling | 13                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Aging of Exploratory Well Costs                                                                                                             | The following table provides a further aging of those exploratory well costs that have been capitalized for a period greater than one year since the commencement of drilling as ofSeptember 30, 2013:Suspended SinceTotal201220112010 & Prior(millions)Country/Project:Offshore Equatorial GuineaCarla$12$—$12$—Diega10614659Felicita361233Yolanda191117Offshore CameroonYoYo483540Offshore IsraelLeviathan125176741Leviathan-1 Deep774928—Tanin 134232—Dolphin 122—22—Dalit231—22Offshore CyprusCyprus A-1701357—Deepwater Gulf of MexicoGunflint11664—52OtherProjects of $10 million or less each2920—9Total$717$172$272$273    
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|                                                                                                                                            | Total                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|(millions)                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Country/Project:                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Offshore Equatorial Guinea                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Carla                                                                                                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Diega                                                                                                                                       | 106                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Felicita                                                                                                                                    | 36                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Yolanda                                                                                                                                     | 19                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Offshore Cameroon                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|YoYo                                                                                                                                        | 48                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Offshore Israel                                                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Leviathan                                                                                                                                   | 125                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Leviathan-1 Deep                                                                                                                            | 77                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Tanin 1                                                                                                                                     | 34                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Dolphin 1                                                                                                                                   | 22                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Dalit                                                                                                                                       | 23                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Offshore Cyprus                                                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Cyprus A-1                                                                                                                                  | 70                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Deepwater Gulf of Mexico                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Gunflint                                                                                                                                    | 116                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Other                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Projects of $10 million or less each                                                                                                        | 29                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Total                                                                                                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

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