Exploratory Costs Exploratory Well Costs (Capitalized Exploratory Costs And the Number Of Projects For Which Exploratory Costs Have Been Capitalized) (Details) $ in Millions	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Capitalized Exploratory Well Costs that Have Been Capitalized for Period of One Year or Less	$ 420		$ 318
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year	23		5
Capitalized Exploratory Well Costs	$ 443	$ 432	$ 323
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects	12		3