Property, Plant and Equipment - Exploratory Drilling Costs Capitalized (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 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	$ 1,232
Year 2013 [Member]
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	74
Year 2012 [Member]
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	373
Year 2011 [Member]
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	338
Year 2010 [Member]
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	211
2009 and prior [Member]
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	$ 236