Derivatives (Classification of Gross Fair Values of Derivative Instruments, Excluding Cash Collateral) (Detail) - Commodity derivatives - USD ($) $ in Millions		Jun. 30, 2021	Dec. 31, 2020
Other current assets
Derivative [Line Items]
Asset		$ 341	$ 88
Liability		382	91
Other current liabilities
Derivative [Line Items]
Asset		0	0
Liability	[1]	14	7
Deferred credits and other liabilities
Derivative [Line Items]
Asset		0	0
Liability	[1]	$ 88	$ 56

[1] Includes embedded derivatives.