Other Assets - Goodwill and Intangible Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill	$ 4,333	$ 4,196
Identifiable Intangible Assets	632	641
Investment Banking [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill	281	281
Global Markets - Fixed Income, Currency and Commodities [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill	269	269
Identifiable Intangible Assets	2	3
Global Markets - Equities [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill	2,645	2,508
Identifiable Intangible Assets	46
Asset Management [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill	390	390
Identifiable Intangible Assets	264	265
Consumer banking [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill	48	48
Identifiable Intangible Assets	6	7
Wealth management [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill	700	700
Identifiable Intangible Assets	$ 314	$ 366