Suspended Exploratory Well Costs (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Capitalized Exploratory Well Costs [Abstract]
Suspended exploratory well costs	$ 1,100	$ 1,200
Unproved Shenandoah Properties [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Suspended exploratory well cost expensed	435
Suspended exploratory well costs previously capitalized for a period greater than one year since the completion of drilling at December 31, 2016, charged to exploration expense	$ 267