|**Asset Impairments (Notes)**                               | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
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|**Asset Impairments [Abstract]**                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Asset Impairments                                           | Asset ImpairmentsPre-tax (non-cash) asset impairment charges were as follows:Three Months Ended September 30,Nine Months EndedSeptember 30,(millions)2015201420152014US Properties, Primarily Shelf and Deepwater Gulf of Mexico$—$2$11$56Eastern Mediterranean—313214North Sea———94Total$—$33$43$164Impairments for 2015 are primarily related to revisions in expected field abandonment or other costs at South Raton and Lorien (Deepwater Gulf of Mexico) and the Noa and Pinnacles fields (Eastern Mediterranean).Impairments for 2014 were primarily related to an increase in expected field abandonment costs and a change in the timing of abandonment activities at the North Sea MacCulloch field.See Note2. Basis of Presentation,Note8. Fair Value Measurements and DisclosuresandNote10. Asset Retirement Obligations.
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|                                                            | Three Months Ended September 30,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(millions)                                                  | 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|US Properties, Primarily Shelf and Deepwater Gulf of Mexico | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Eastern Mediterranean                                       | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|North Sea                                                   | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Total                                                       | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    

X- DefinitionAsset Impairments [Abstract]
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