|**Capitalized Exploratory Well Costs and Undeveloped Leasehold 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:(millions)Three Months Ended March 31, 2017Capitalized Exploratory Well Costs, Beginning of Period$768Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves6Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves(1)(203)Capitalized Exploratory Well Costs, End of Period$571(1)Amount relates to the approval and sanction of the first phase of development of the Leviathan field offshore Israel.
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|(millions)                                                                                              | Three Months Ended March 31, 2017                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Capitalized Exploratory Well Costs, Beginning of Period                                                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves                | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves(1)              | (203                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Capitalized Exploratory Well Costs, End of Period                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|(1)                                                                                                     | Amount relates to the approval and sanction of the first phase of development of the Leviathan field offshore Israel.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Aging of Capitalized Well Costs                                                                         | The following table provides an aging of capitalized exploratory well costs based on the date that drilling commenced:(millions)March 31, 2017December 31, 2016Exploratory Well Costs Capitalized for a Period of One Year or Less$58$69Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling(1)513699Balance at End of Period$571$768                                                                                                                                                                                                                                          
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|(millions)                                                                                              | March 31, 2017                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|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(1) | 513                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Balance at End of Period                                                                                | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Aging of Exploratory Well Costs                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

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