Loans - Impaired Financing Receivables (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Nonaccrual loans	$ 3,543	$ 1,530
Nonaccrual loans divided by gross loans at amortized cost	3.60%	1.70%
Corporate [Member]
Financing Receivable, Impaired [Line Items]
Nonaccrual loans	$ 2,804	$ 1,122
Wealth management [Member]
Financing Receivable, Impaired [Line Items]
Nonaccrual loans	47	52
Commercial real estate [Member]
Financing Receivable, Impaired [Line Items]
Nonaccrual loans	446	175
Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Nonaccrual loans	27	143
Installment [Member]
Financing Receivable, Impaired [Line Items]
Nonaccrual loans	32	$ 38
Other [Member]
Financing Receivable, Impaired [Line Items]
Nonaccrual loans	$ 187