Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 817	$ 602
Accruing Loans Contractually Past Due 90 Days or More	4	6
Nonaccrual Loans With No Allowance For Credit Losses	201	205
Residential mortgage loans carried at lower of cost or fair value of the collateral less cost to sell	103	108
Commercial loans
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	644	424
Accruing Loans Contractually Past Due 90 Days or More	0	1
Nonaccrual Loans With No Allowance For Credit Losses	119	119
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	228	229
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	41	40
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	170	143
Accruing Loans Contractually Past Due 90 Days or More	0	1
Nonaccrual Loans With No Allowance For Credit Losses	34	29
Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	246	49
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	44	48
Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans		3
Accruing Loans Contractually Past Due 90 Days or More		0
Nonaccrual Loans With No Allowance For Credit Losses		2
Consumer loans
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	173	178
Accruing Loans Contractually Past Due 90 Days or More	4	5
Nonaccrual Loans With No Allowance For Credit Losses	82	86
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	167	172
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	77	81
Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	6	6
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	5	5
Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Accruing Loans Contractually Past Due 90 Days or More	3	3
Nonaccrual Loans With No Allowance For Credit Losses	0	0
Consumer loans | Other consumer
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