Loans - Summary of Financing receivable, past due (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	$ 474	$ 804
Past due loans divided by gross loans at amortized cost	0.30%	0.80%
Corporate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	$ 95	$ 294
Wealth management [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	20	92
Commercial real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	150	232
Residential real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	7	27
Installment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	27	58
Credit Card Receivable [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	157	77
Other [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	18	24
30-89 days [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	136	219
30-89 days [Member] \| Corporate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	5	0
30-89 days [Member] \| Wealth management [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	0	58
30-89 days [Member] \| Commercial real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	7	49
30-89 days [Member] \| Residential real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	3	4
30-89 days [Member] \| Installment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	20	42
30-89 days [Member] \| Credit Card Receivable [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	86	46
30-89 days [Member] \| Other [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	15	20
90 days or more [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	338	585
90 days or more [Member] \| Corporate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	90	294
90 days or more [Member] \| Wealth management [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	20	34
90 days or more [Member] \| Commercial real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	143	183
90 days or more [Member] \| Residential real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	4	23
90 days or more [Member] \| Installment [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	7	16
90 days or more [Member] \| Credit Card Receivable [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	71	31
90 days or more [Member] \| Other [Member]
Financing Receivable, Past Due [Line Items]
Financing receivable, past due	$ 3	$ 4