Suspended Exploratory Well Costs (Detail) (USD $)			9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Greater Than One Year [Member]
Capitalized Exploratory Well Costs [Abstract]
Suspended exploratory well costs	$ 2,200,000,000	$ 2,100,000,000
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Exploratory well costs previously capitalized as suspended exploratory well costs for greater than one year at December 31, 2012, charged to dry hole expense			$ 95,000,000