Derivatives - Effect of Commodity Derivative Instruments in Statements of Income (Detail) - Commodity derivatives - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ 139	$ 155	$ 125	$ (12)
Sales and other operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	(1)	10	10	18
Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ 140	$ 145	$ 115	$ (30)