Fair Value Measurements and Disclosures - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 14, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairments	$ 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