Derivatives (Classification Of Gross Fair Values Of Derivative Instruments, Excluding Cash Collateral) (Detail) - Commodity derivative instruments - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Other current assets
Derivatives, Fair Value [Line Items]
Asset		$ 400	$ 127
Liability		283	126
Other current liabilities(a)
Derivatives, Fair Value [Line Items]
Asset	[1]	1	0
Liability	[1]	16	14
Deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Asset	[1]	0	0
Liability	[1]	$ 54	$ 52

[1] Includes embedded derivatives.