Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 523	$ 435
Accruing Loans Contractually Past Due 90 Days or More	4	4
Nonaccrual Loans With No Allowance For Credit Losses	220	229
Residential mortgage loans carried at lower of cost or fair value of the collateral less cost to sell	120	109
Commercial loans
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	308	215
Accruing Loans Contractually Past Due 90 Days or More	1	1
Nonaccrual Loans With No Allowance For Credit Losses	125	145
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	107	45
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	43	43
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	145	116
Accruing Loans Contractually Past Due 90 Days or More	1	1
Nonaccrual Loans With No Allowance For Credit Losses	28	62
Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	55	54
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	53	40
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	215	220
Accruing Loans Contractually Past Due 90 Days or More	3	3
Nonaccrual Loans With No Allowance For Credit Losses	95	84
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	204	213
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	90	79
Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	11	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
Accruing Loans Contractually Past Due 90 Days or More		1
Nonaccrual Loans With No Allowance For Credit Losses		$ 0