Commitments and Contingencies - Minimum Commitments Due (Details) $ in Millions	Dec. 31, 2017 USD ($)
Other Commitments [Line Items]
2018	$ 969
2019	497
2020	361
2021	297
2022	244
2023 and Thereafter	1,667
Total	4,035
Drilling, Equipment, and Purchase Obligations
Other Commitments [Line Items]
2018	636
2019	167
2020	40
2021	13
2022	8
2023 and Thereafter	32
Total	896
Transportation and Gathering Obligations
Other Commitments [Line Items]
2018	215
2019	252
2020	247
2021	223
2022	182
2023 and Thereafter	1,355
Total	2,474
Operating Lease Obligations
Other Commitments [Line Items]
2018	44
2019	33
2020	32
2021	32
2022	33
2023 and Thereafter	156
Total	330
Capital Lease and Other Obligations
Other Commitments [Line Items]
2018	74
2019	45
2020	42
2021	29
2022	21
2023 and Thereafter	124
Total	$ 335