Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 428	$ 617
Accruing Loans Contractually Past Due 90 Days or More	2	3
Nonaccrual Loans With No Allowance For Credit Losses	175	211
Residential mortgage loans carried at lower of cost or fair value of the collateral less cost to sell	63	86
Commercial loans:
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	291	379
Accruing Loans Contractually Past Due 90 Days or More	1	1
Nonaccrual Loans With No Allowance For Credit Losses	134	152
Commercial loans: | Real Estate, including Construction
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	92	140
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	18	20
Commercial loans: | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	107	134
Accruing Loans Contractually Past Due 90 Days or More	1	1
Nonaccrual Loans With No Allowance For Credit Losses	52	69
Commercial loans: | Global banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	91	105
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	63	63
Commercial loans: | Other commercial:
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	1
Accruing Loans Contractually Past Due 90 Days or More	0
Nonaccrual Loans With No Allowance For Credit Losses	1
Consumer loans:
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	137	238
Accruing Loans Contractually Past Due 90 Days or More	1	2
Nonaccrual Loans With No Allowance For Credit Losses	41	59
Consumer loans: | Residential mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	131	229
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	38	55
Consumer loans: | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	6	9
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	3	4
Consumer loans: | Credit cards
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Accruing Loans Contractually Past Due 90 Days or More	1	2
Nonaccrual Loans With No Allowance For Credit Losses	$ 0	$ 0