|**Asset Impairments (Notes)**    | 3 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 March 31,(millions)20152014Deepwater Gulf of Mexico3—Eastern Mediterranean24—North Sea—92Non-Core US Property—5Total$27$97Impairments for 2015 were related to facility costs at South Raton (Deepwater Gulf of Mexico) and increases in expected field abandonment costs for 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 MacCulloch North Sea field.See Note2. Basis of Presentation,Note7. Fair Value Measurements and DisclosuresandNote9. Asset Retirement Obligations.
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|                                 | Three Months Ended March 31,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|(millions)                       | 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Deepwater Gulf of Mexico         | 3                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Eastern Mediterranean            | 24                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|North Sea                        | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Non-Core US Property             | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Total                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              

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