Exploratory Well Costs (Aging Of Capitalized Exploratory Well Costs Based On The Date Of Drilling) (Detail) $ in Millions	Sep. 30, 2017 USD ($) Number	Dec. 31, 2016 USD ($) Number
Disclosure Exploratory Well Costs Aging Of Capitalized Exploratory Well Costs Based On The Date Of Drilling [Abstract]
Capitalized exploratory well costs that have been capitalized for a period of one year or less	$ 266	$ 141
Capitalized exploratory well costs that have been capitalized for a period greater than one year	4	10
Total capitalized exploratory well costs	$ 270	$ 151
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects | Number	4	8