Accounting For Suspended Exploratory Well Costs (Narrative) (Details) $ in Millions	Dec. 31, 2018 USD ($) Projects	Dec. 31, 2017 USD ($) Projects	Dec. 31, 2016 USD ($) Projects	Dec. 31, 2015 USD ($)
Exploratory Wells Drilled [Line Items]
Number of projects that have exploratory well costs capitalized for a period of greater than one year	52	46	58
Number of projects that have drilling in the preceding twelve months or exploratory activity planned in the next two years as of December 31, 2018	12
Number of projects with completed exploratory activity progressing toward development as of December 31, 2018	40
Capitalized exploratory well costs | $	$ 4,160	$ 3,700	$ 4,477	$ 4,372
40 Projects [Member]
Exploratory Wells Drilled [Line Items]
Capitalized exploratory well costs | $	$ 2,543