Derivatives - Effect of Commodity Derivative Instruments in Statements of Income (Detail) (Commodity derivatives, USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (116)	$ 54	$ (167)	$ (5)
Sales and other operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	(2)	3	8	4
Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (114)	$ 51	$ (175)	$ (9)