Derivative Financial Instruments - Gains and Losses on Derivative Instruments Held For Trading Purpose (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ (27)	$ 116	$ (475)	$ 18
Trading revenue (expense) [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	45	773	197	655
Trading revenue (expense) [Member] | Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(56)	(355)	112	(1,164)
Trading revenue (expense) [Member] | Equity contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(20)	(385)	(1,000)	683
Trading revenue (expense) [Member] | Precious metals contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	74	67	115	450
Trading revenue (expense) [Member] | Credit contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ (70)	$ 16	$ 101	$ (606)