Property, Plant and Equipment (Schedule of Aging of Capitalized Exploratory Well Costs (Details) $ in Millions	Dec. 31, 2017 USD ($) Project	Dec. 31, 2016 USD ($) Project	Dec. 31, 2015 USD ($) Project	Dec. 31, 2014 USD ($)
Schedule Of Aging Of Capitalized Exploratory Well Costs [Abstract]
Exploratory well costs capitalized for a period of one year or less	$ 113	$ 88	$ 60
Exploratory well costs capitalized for a period greater than one year	200	173	165
Ending balance	$ 313	$ 261	$ 225	$ 199
Number of projects with exploratory well costs capitalized for a period greater than one year | Project	2	2	2