Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Guarantor Obligations [Line Items]
Override Royalty - GOM Future Abandonment		$ 70
Payments to Acquire Property, Plant, and Equipment [Abstract]
Commitments to acquire property, plant and equipment	$ 102	$ 57
UK Government [Member] | Foreign Tax Authority [Member]
Guarantor Obligations [Line Items]
Income Tax Examination, Penalties and Interest Expense	$ 108