Fair Value Measurements and Disclosures - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 14, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairments	$ 0		$ 0	$ 168	$ 0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Tamar and Dalit Fields
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount percent						15.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf of Mexico Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairments		$ 168		$ 168