Trading Assets and Liabilities - Gains and Losses from Market Making (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Trading activity, gains and losses, net [Line Items]
Market making	$ 3,327	$ 2,476	$ 12,796	$ 7,678
Interest Rates [Member]
Trading activity, gains and losses, net [Line Items]
Market making	1,732	(613)	3,784	1,379
Credit [Member]
Trading activity, gains and losses, net [Line Items]
Market making	578	245	3,571	700
Currencies [Member]
Trading activity, gains and losses, net [Line Items]
Market making	(981)	2,127	(1,674)	3,549
Equities [Member]
Trading activity, gains and losses, net [Line Items]
Market making	1,391	788	5,022	1,963
Commodities [Member]
Trading activity, gains and losses, net [Line Items]
Market making	$ 607	$ (71)	$ 2,093	$ 87