Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 602	$ 435
Accruing Loans Contractually Past Due 90 Days or More	6	4
Nonaccrual Loans With No Allowance For Credit Losses	205	229
Residential mortgage loans carried at lower of cost or fair value of the collateral less cost to sell	108	109
Commercial loans
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	424	215
Accruing Loans Contractually Past Due 90 Days or More	1	1
Nonaccrual Loans With No Allowance For Credit Losses	119	145
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	229	45
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	40	43
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	143	116
Accruing Loans Contractually Past Due 90 Days or More	1	1
Nonaccrual Loans With No Allowance For Credit Losses	29	62
Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	49	54
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	48	40
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	178	220
Accruing Loans Contractually Past Due 90 Days or More	5	3
Nonaccrual Loans With No Allowance For Credit Losses	86	84
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	172	213
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	81	79
Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	6	7
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	2
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	2	1
Nonaccrual Loans With No Allowance For Credit Losses	$ 0	$ 0