|**Asset Retirement Obligations**                                     | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
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|**Asset Retirement Obligation Disclosure [Abstract]**                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Asset Retirement Obligations                                         | Note9.  Asset Retirement ObligationsAsset retirement obligations (AROs) consist primarily of estimated costs of dismantlement, removal, site reclamation and similar activities associated with our oil and gas properties. Changes in AROs were as follows:Year Ended December 31,(millions)20172016Asset Retirement Obligations, Beginning Balance$935$989Liabilities Incurred9421Liabilities Settled(82)(120)Revision of Estimate(65)(3)Reclassification to Liabilities Associated with Assets Held for Sale(54)—Accretion Expense4748Asset Retirement Obligations, Ending Balance$875$935Year Ended December 31, 2017Liabilities incurred include$63 millionrelated to the Clayton Williams Energy Acquisition and$31 millionprimarily for other US onshore wells and midstream facilities placed into service.Liabilities settled include$43 millionrelated to abandonment of US onshore properties,$19 millionrelated to properties sold in the Greeley Crescent (DJ Basin) acreage divestiture,$12 millionrelated to properties sold in the Marcellus Shale upstream divestiture and$8 millionrelated to other offshore domestic and international properties.Revisions of estimates include a$42 milliondecrease related to changes in cost and timing associated with the North Sea abandonment project and a$38 milliondecrease for US onshore and Gulf of Mexico properties, partially offset by an increase of$15 millionfor West Africa.In 2017, we also transferred$42 millionand$12 millionof ARO liabilities associated with Southwest Royalties and Tamar field, offshore Israel, respectively, to liabilities associated with assets held for sale. Refer toItem 8. Financial Statements and Supplementary Data - Note 4. Acquisitions, Divestitures and Merger.Year Ended December 31, 2016Liabilities incurred were due to new wells and facilities placed into service for US onshore, Gulf of Mexico, and offshore Israel.Liabilities settled were related to wells and facilities permanently abandoned at the end of their useful lives and to assets sold. Settlements included $65 millionrelated to abandonment of Gulf of Mexico properties,$49 millionrelated to US onshore properties abandoned or sold,$5 millionrelated to offshore Israel properties and$1 millionrelated to the North Sea.
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|                                                                     | Year Ended December 31,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(millions)                                                           | 2017                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Asset Retirement Obligations, Beginning Balance                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Liabilities Incurred                                                 | 94                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Liabilities Settled                                                  | (82                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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|Reclassification to Liabilities Associated with Assets Held for Sale | (54                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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|Asset Retirement Obligations, Ending Balance                         | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

X- ReferencesNo definition available.
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duration X- DefinitionThe entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -URI http://asc.fasb.org/subtopic&trid=2175671
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