|**Capitalized Exploratory Well Costs (Tables)**                                                                                             | 3 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:Three Months Ended March 31, 2013(millions)Capitalized Exploratory Well Costs, Beginning of Period$900Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves178Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves(8)Capitalized Exploratory Well Costs, End of Period$1,070                                                                                                                         
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|                                                                                                                                            | Three Months Ended March 31, 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|(millions)                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Capitalized Exploratory Well Costs, Beginning of Period                                                                                     | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves                                                    | 178                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves                                                     | (8                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|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:March 31, 2013December 31, 2012(millions)Exploratory Well Costs Capitalized for a Period of One Year or Less$453$355Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling617545Balance at End of Period$1,070$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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|                                                                                                                                            | March 31, 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                                        | 617                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|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 ofMarch 31, 2013:Suspended SinceTotal201220112010 & Prior(millions)Country/Project:Offshore Equatorial GuineaCarla$12$—$12$—Diega10614659Felicita361233Yolanda18—117Offshore CameroonYoYo472540Offshore IsraelLeviathan11356741Leviathan-1 Deep552728—Tanin 133231—Dolphin 122—22—Dalit22——22Offshore CyprusCyprus A-164757—Deepwater Gulf of MexicoGunflint7723—54OtherProjects of $10 million or less each123—9Total$617$71$271$275         
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|                                                                                                                                            | Total                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|(millions)                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Country/Project:                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Offshore Equatorial Guinea                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Carla                                                                                                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Diega                                                                                                                                       | 106                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Felicita                                                                                                                                    | 36                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Yolanda                                                                                                                                     | 18                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Offshore Cameroon                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|YoYo                                                                                                                                        | 47                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Offshore Israel                                                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Leviathan                                                                                                                                   | 113                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Leviathan-1 Deep                                                                                                                            | 55                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Tanin 1                                                                                                                                     | 33                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Dolphin 1                                                                                                                                   | 22                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Dalit                                                                                                                                       | 22                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Offshore Cyprus                                                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Cyprus A-1                                                                                                                                  | 64                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Deepwater Gulf of Mexico                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Gunflint                                                                                                                                    | 77                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Other                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Projects of $10 million or less each                                                                                                        | 12                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Total                                                                                                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              

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