Asset Impairments - Pre-tax (Non-Cash) Asset Impairment Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairments	$ 70	$ 92	$ 533
Gulf of Mexico
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairments	63	0	158
Israel
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairments	0	88	36
Equatorial Guinea
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairments	0	0	339
Other International
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairments	$ 7	$ 4	$ 0