|**Commitments and Contingencies (Tables)**              | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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|**Commitments and Contingencies Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Minimum commitments                                     | Minimum commitments as ofDecember 31, 2015consist of the following:(millions)Drilling, Equipment,and Purchase ObligationsTransportationand Gathering ObligationsOperatingLeaseObligationsCapitalLease and Other Obligations(1)Total2016$291$217$42$76$626201716724844815402018223143979454201916305265039720201027026473532021 and Thereafter91,8161681792,172Total$515$3,170$345$512$4,542(1)Annual lease payments, net to our interest, exclude regular maintenance and operational costs.See Note10.  Long-Term Debt.
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|(millions)                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2016                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2017                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2018                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2019                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2020                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|2021 and Thereafter                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

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duration X- DefinitionTabular disclosure of the aggregate amount of payments due on known contractual obligations for the five years following the date of the latest balance sheet and the combined aggregate amount of maturities of known contractual obligations.
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