Exploratory Costs Exploratory Well Costs (Capitalized Exploratory Costs And the Number Of Projects For Which Exploratory Costs Have Been Capitalized) (Details) $ in Millions	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Property, Plant and Equipment [Line Items]
Capitalized Exploratory Well Costs that Have Been Capitalized for Period of One Year or Less	$ 396		$ 303
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year	2		3
Capitalized Exploratory Well Costs	$ 398	$ 357	$ 306
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects	1		1