Other Assets - Other Assets (Parenthetical) (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Other Assets [Line Items]
Accumulated depreciation and amortization	$ 10,040	$ 9,950
Property, leasehold improvements and equipment used for operation	6,490	6,160
Foreclosed real estate included in property, leasehold improvements and equipment	$ 346	$ 521
Amortization period - Capitalized costs of software developed or obtained for internal use	3 years	3 years
Operating lease right-of-use assets	$ 2,268	$ 2,360
Investments in qualified affordable housing projects	684	606
Asset Management [Member]
Schedule Of Other Assets [Line Items]
Assets classified as held for sale	1,330	470
European headquarters in London [Member]
Schedule Of Other Assets [Line Items]
Operating lease right-of-use assets	$ 152	$ 885