Exploratory Well Costs (Capitalized Exploratory Costs And the Number Of Projects For Which Exploratory Costs Have Been Capitalized) (Details) $ in Millions	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Capitalized exploratory well costs that have been suspended:
One year or less	$ 660	$ 509	$ 493
More than one year	0	0	12
Total	$ 660	$ 509	$ 505
Number of projects with exploratory well costs that have been suspended for a period greater than one year	0	0	7