Derivative Financial Instruments - Gains and Losses on Derivative Instruments Held For Trading Purpose (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives		$ (210)	$ (88)	$ (98)		$ (240)
Trading revenue [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives		(135)	(171)	(118)		(115)
Trading revenue [Member] | Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives		(144)	253	(809)	[1]	239	[1]
Trading revenue [Member] | Equity contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives		(189)	(61)	1,068		(150)
Trading revenue [Member] | Precious metals contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives		223	36	383	[1]	53	[1]
Trading revenue [Member] | Credit contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives		$ 35	(145)	$ (622)		(267)
Reclassified Amount [Member] | Trading revenue [Member] | Precious metals contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	[1]		$ 424			$ 575

[1] During the third quarter of 2019, we changed our presentation for certain derivatives that were previously reported in foreign exchange contracts and began reporting these derivatives in precious metals contracts. As a result, we have reclassified $424 million and $575 million of gains from foreign exchange contracts to precious metals contracts during the three and six months ended June 30, 2019, respectively, to conform with the current year presentation.