|**Property Transactions (Tables)**                             | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                              
|-------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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|Schedule of Disposal Groups, Gain on Divestitures - Onshore US | The information regarding the assets sold is as follows:Year Ended December 31,(millions)201420132012Cash Proceeds$135$150$1,044LessNet Book Value of Assets Sold(150)(117)(836)Goodwill Allocated to Assets Sold(7)(8)(61)Asset Retirement Obligations Associated with Assets Sold48820Other Closing Adjustments103(13)Gain on Divestitures$36$36$154                                                                                                       
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|                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|(millions)                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Cash Proceeds                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Less                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net Book Value of Assets Sold                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Goodwill Allocated to Assets Sold                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Asset Retirement Obligations Associated with Assets Sold       |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Other Closing Adjustments                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Gain on Divestitures                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Schedule of Disposal Groups, Gain on Divestitures - China      | The information regarding the China assets sold is as follows:Year Ended December 31, 2014(millions)2014Sales Proceeds$186LessNet Book Value of Assets Sold(149)Other Closing Adjustments(2)Gain on Divestiture$35                                                                                                                                                                                                                                           
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|                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|                                                               | Year Ended December 31, 2014                                                                                                                                                                                                                                                                                                                                                                                                                                 
|(millions)                                                     | 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Sales Proceeds                                                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Less                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Net Book Value of Assets Sold                                  | (149                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other Closing Adjustments                                      | (2                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Gain on Divestiture                                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|North Sea Assets [Member]                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Summary of Discontinued Operations                             | Summarized results of discontinued operations are as follows:Year Ended December 31,(millions)20132012Oil and Gas Sales$37$208Income Before Income Taxes(1)12101Income Tax Expense655Operating Income, Net of Tax646Gain on Sale, Net of Tax6516Discontinued Operations, Net of Tax$71$62(1)Income before income taxes for 2012 includes exploration expense of$27 millionrelated to the Selkirk field which was determined uneconomic for joint development.
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|                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|                                                               | Year Ended December 31,                                                                                                                                                                                                                                                                                                                                                                                                                                      
|(millions)                                                     | 2013                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Oil and Gas Sales                                              | $                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Income Before Income Taxes(1)                                  | 12                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Income Tax Expense                                             | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Operating Income, Net of Tax                                   | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Gain on Sale, Net of Tax                                       | 65                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Discontinued Operations, Net of Tax                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                            

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