Property, Plant and Equipment - Exploratory Drilling Costs Capitalized (Detail) $ in Millions	Dec. 31, 2018 USD ($)
Projects With Exploratory Well Costs Capitalized For More Than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	$ 267
Year 2017
Projects With Exploratory Well Costs Capitalized For More Than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	97
Year 2016
Projects With Exploratory Well Costs Capitalized For More Than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	0
Year 2015
Projects With Exploratory Well Costs Capitalized For More Than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	166
Year 2014
Projects With Exploratory Well Costs Capitalized For More Than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	0
Year 2013
Projects With Exploratory Well Costs Capitalized For More Than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	$ 4