|**Capitalized Exploratory Well Costs (Tables)**                                                                                             | 6 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:Six Months Ended June 30, 2013(millions)Capitalized Exploratory Well Costs, Beginning of Period$900Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves313Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves(18)Capitalized Exploratory Well Costs Charged to Expense(3)Capitalized Exploratory Well Costs, End of Period$1,192                                                                  
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|                                                                                                                                            | Six Months Ended June 30, 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|(millions)                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Capitalized Exploratory Well Costs, Beginning of Period                                                                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves                                                    | 313                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves                                                     | (18                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|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:June 30, 2013December 31, 2012(millions)Exploratory Well Costs Capitalized for a Period of One Year or Less$523$355Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling669545Balance at End of Period$1,192$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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|                                                                                                                                            | June 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                                        | 669                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|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 ofJune 30, 2013:Suspended SinceTotal201220112010 & Prior(millions)Country/Project:Offshore Equatorial GuineaCarla$12$—$12$—Diega105—4659Felicita361233Yolanda18—117Offshore CameroonYoYo505540Offshore IsraelLeviathan128206741Leviathan-1 Deep714328—Tanin 134232—Dolphin 122—22—Dalit22——22Offshore CyprusCyprus A-165857—Deepwater Gulf of MexicoGunflint8735—52OtherProjects of $10 million or less each1910—9Total$669$124$272$273      
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|                                                                                                                                            | Total                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|(millions)                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Country/Project:                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Offshore Equatorial Guinea                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Carla                                                                                                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Diega                                                                                                                                       | 105                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Felicita                                                                                                                                    | 36                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Yolanda                                                                                                                                     | 18                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Offshore Cameroon                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|YoYo                                                                                                                                        | 50                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Offshore Israel                                                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Leviathan                                                                                                                                   | 128                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Leviathan-1 Deep                                                                                                                            | 71                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Tanin 1                                                                                                                                     | 34                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Dolphin 1                                                                                                                                   | 22                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Dalit                                                                                                                                       | 22                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Offshore Cyprus                                                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Cyprus A-1                                                                                                                                  | 65                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Deepwater Gulf of Mexico                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Gunflint                                                                                                                                    | 87                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Projects of $10 million or less each                                                                                                        | 19                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total                                                                                                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

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