|**Commitments and Contingencies (Tables)**              | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
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|**Commitments and Contingencies Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Other Commitments                                       | Minimum commitments have been updated to give effect to the Clayton Williams Energy Acquisition, the Marcellus Shale upstream divestiture, as well as commitments related to Leviathan development activities, and consist of the following as of June 30, 2017:(millions)Drilling, Equipment,and Purchase ObligationsTransportationand Gathering Obligations(1)OperatingLeaseObligationsCapitalLease Obligations(2)TotalJuly - December 2017$306$116$24$39$485201834124747747092019146276354550220202225033423472021421334292802022 and Thereafter331,4961981451,872Total$852$2,598$371$374$4,195(1)Includes$1.6 billionof future cash payments related to retained Marcellus Shale firm transportation contracts. See discussion above.(2)Annual lease payments, net to our interest, exclude regular maintenance and operating costs. SeeNote6. Debt.
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|(millions)                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|July - December 2017                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2018                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2019                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2020                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2021                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2022 and Thereafter                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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|(1)                                                     | Includes$1.6 billionof future cash payments related to retained Marcellus Shale firm transportation contracts. See discussion above.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
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|(2)                                                     | Annual lease payments, net to our interest, exclude regular maintenance and operating costs. SeeNote6. Debt.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            

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