Commitments and Contingencies Commitments and Contingencies - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Long-term Purchase Commitment [Line Items]
Purchase Obligation Agreement Expiration Date	2028
Future Drilling Commitments At Balance Sheet Date	$ 97
Drilling Commitments Year One	42
Drilling Commitments Year Two	41
Drilling Commitments Year Three	10
Drilling Commitments Year Four	4
Purchase Obligation	1,400
Purchase Obligation, Future Minimum Payments, Remainder of Fiscal Year	112
Purchase Obligation, Due in Second Year	225
Purchase Obligation, Due in Third Year	194
Purchase Obligation, Due in Fourth Year	175
Purchase Obligation, Due in Fifth Year	168
Purchase Obligation, Due after Fifth Year	$ 487
Future Drilling Commitments End Date	2021-06