Derivatives (Effect Of Commodity Derivative Instruments In Statements Of Income) (Detail) - Commodity derivative instruments - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (46)	$ (21)	$ (180)
Sales and other operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	13	5	(13)
Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (59)	$ (26)	$ (167)