Reconciliation of Current Period Changes, Net of Applicable Income Taxes, for Derivatives Qualifying as Hedges (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments [Abstract]
Derivatives qualifying as effective accounting hedges, beginning of period	$ 2,677	$ 1,983	$ 2,002	$ 1,781
Cumulative effect of changes in accounting:
Current period increases (decreases) in fair value, net of deferred taxes	(191)	306	544	560
Reclassification to net (income) loss, net of deferred taxes	(35)	(30)	(95)	(82)
Derivatives qualifying as effective accounting hedges, end of period	$ 2,451	$ 2,259	$ 2,451	$ 2,259