Derivative Financial Instruments - Gains and Losses on Derivative Instruments Held For Trading Purpose (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ 401	$ 112
Trading revenue [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	429	17
Trading revenue [Member] | Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	116	(665)
Trading revenue [Member] | Equity contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(279)	1,257
Trading revenue [Member] | Precious metals contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(80)	160
Trading revenue [Member] | Credit contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ 215	$ (657)