Loans - Status of Loan Portfolios (Detail) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total	[1]	$ 59,797	$ 58,987
Commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		498	4,656
One year prior to current year		4,592	3,868
Two years prior to current year		3,720	3,250
Three years prior to current year		3,317	1,388
Four years prior to current year		1,380	2,354
Prior		12,688	11,069
Revolving Loans		13,784	13,054
Revolving Loans Converted to Term Loans		326	318
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		40,305	39,957
Commercial loans | Real estate, including construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		164	920
One year prior to current year		982	1,286
Two years prior to current year		1,286	1,019
Three years prior to current year		1,040	355
Four years prior to current year		319	1,054
Prior		3,237	2,409
Revolving Loans		40	41
Revolving Loans Converted to Term Loans		3	3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		7,071	7,087
Commercial loans | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		237	1,270
One year prior to current year		1,284	1,148
Two years prior to current year		1,028	1,074
Three years prior to current year		1,307	231
Four years prior to current year		224	561
Prior		4,492	4,253
Revolving Loans		7,202	6,922
Revolving Loans Converted to Term Loans		273	265
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		16,047	15,724
Commercial loans | Global banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		82	2,255
One year prior to current year		2,162	1,153
Two years prior to current year		1,128	844
Three years prior to current year		761	151
Four years prior to current year		204	321
Prior		3,796	3,600
Revolving Loans		2,339	2,351
Revolving Loans Converted to Term Loans		50	50
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		10,522	10,725
Commercial loans | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		15	211
One year prior to current year		164	281
Two years prior to current year		278	313
Three years prior to current year		209	651
Four years prior to current year		633	418
Prior		1,163	807
Revolving Loans		4,203	3,740
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		6,665	6,421
Commercial loans | Performing loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		498	4,656
One year prior to current year		4,592	3,833
Two years prior to current year		3,720	3,250
Three years prior to current year		3,283	1,388
Four years prior to current year		1,380	2,314
Prior		12,194	10,822
Revolving Loans		13,668	12,951
Revolving Loans Converted to Term Loans		326	318
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		39,661	39,532
Commercial loans | Performing loans | Real estate, including construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		164	920
One year prior to current year		982	1,286
Two years prior to current year		1,286	1,019
Three years prior to current year		1,040	355
Four years prior to current year		319	1,014
Prior		3,030	2,242
Revolving Loans		19	19
Revolving Loans Converted to Term Loans		3	3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		6,843	6,858
Commercial loans | Performing loans | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		237	1,270
One year prior to current year		1,284	1,113
Two years prior to current year		1,028	1,074
Three years prior to current year		1,273	231
Four years prior to current year		224	561
Prior		4,438	4,215
Revolving Loans		7,120	6,851
Revolving Loans Converted to Term Loans		273	265
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		15,877	15,580
Commercial loans | Performing loans | Global banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		82	2,255
One year prior to current year		2,162	1,153
Two years prior to current year		1,128	844
Three years prior to current year		761	151
Four years prior to current year		204	321
Prior		3,563	3,561
Revolving Loans		2,326	2,341
Revolving Loans Converted to Term Loans		50	50
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		10,276	10,676
Commercial loans | Performing loans | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		15	211
One year prior to current year		164	281
Two years prior to current year		278	313
Three years prior to current year		209	651
Four years prior to current year		633	418
Prior		1,163	804
Revolving Loans		4,203	3,740
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		6,665	6,418
Commercial loans | Nonaccrual loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	35
Two years prior to current year		0	0
Three years prior to current year		34	0
Four years prior to current year		0	40
Prior		494	247
Revolving Loans		116	102
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		644	424
Commercial loans | Nonaccrual loans | Real estate, including construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	40
Prior		207	167
Revolving Loans		21	22
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		228	229
Commercial loans | Nonaccrual loans | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	35
Two years prior to current year		0	0
Three years prior to current year		34	0
Four years prior to current year		0	0
Prior		54	38
Revolving Loans		82	70
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		170	143
Commercial loans | Nonaccrual loans | Global banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	0
Prior		233	39
Revolving Loans		13	10
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		246	49
Commercial loans | Nonaccrual loans | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0
One year prior to current year			0
Two years prior to current year			0
Three years prior to current year			0
Four years prior to current year			0
Prior			3
Revolving Loans			0
Revolving Loans Converted to Term Loans			0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total			3
Commercial loans | Accruing loans contractually past due 90 days or more
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0
One year prior to current year			0
Two years prior to current year			0
Three years prior to current year			0
Four years prior to current year			0
Prior			0
Revolving Loans			1
Revolving Loans Converted to Term Loans			0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total			1
Commercial loans | Accruing loans contractually past due 90 days or more | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0
One year prior to current year			0
Two years prior to current year			0
Three years prior to current year			0
Four years prior to current year			0
Prior			0
Revolving Loans			1
Revolving Loans Converted to Term Loans			0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total			1
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		809	2,726
One year prior to current year		2,649	2,841
Two years prior to current year		2,818	4,125
Three years prior to current year		4,090	2,799
Four years prior to current year		2,763	1,272
Prior		6,166	5,061
Revolving Loans		197	206
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		19,492	19,030
Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		799	2,646
One year prior to current year		2,569	2,764
Two years prior to current year		2,742	4,107
Three years prior to current year		4,071	2,770
Four years prior to current year		2,737	1,244
Prior		5,907	4,810
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		18,825	18,341
Consumer loans | Home equity mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		10	80
One year prior to current year		80	69
Two years prior to current year		69	11
Three years prior to current year		10	22
Four years prior to current year		20	25
Prior		193	182
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		382	389
Consumer loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	0
Prior		0	0
Revolving Loans		189	199
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		189	199
Consumer loans | Consumer Portfolio Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	8
Two years prior to current year		7	7
Three years prior to current year		9	7
Four years prior to current year		6	3
Prior		66	69
Revolving Loans		8	7
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		96	101
Consumer loans | Performing loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		809	2,726
One year prior to current year		2,649	2,830
Two years prior to current year		2,808	4,114
Three years prior to current year		4,080	2,790
Four years prior to current year		2,753	1,264
Prior		6,022	4,920
Revolving Loans		194	203
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		19,315	18,847
Consumer loans | Performing loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		799	2,646
One year prior to current year		2,569	2,753
Two years prior to current year		2,732	4,096
Three years prior to current year		4,061	2,761
Four years prior to current year		2,727	1,236
Prior		5,770	4,677
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		18,658	18,169
Consumer loans | Performing loans | Home equity mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		10	80
One year prior to current year		80	69
Two years prior to current year		69	11
Three years prior to current year		10	22
Four years prior to current year		20	25
Prior		187	176
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		376	383
Consumer loans | Performing loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	0
Prior		0	0
Revolving Loans		186	196
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		186	196
Consumer loans | Performing loans | Consumer Portfolio Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	8
Two years prior to current year		7	7
Three years prior to current year		9	7
Four years prior to current year		6	3
Prior		65	67
Revolving Loans		8	7
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		95	99
Consumer loans | Nonaccrual loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	11
Two years prior to current year		10	11
Three years prior to current year		10	9
Four years prior to current year		10	8
Prior		143	139
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		173	178
Consumer loans | Nonaccrual loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	11
Two years prior to current year		10	11
Three years prior to current year		10	9
Four years prior to current year		10	8
Prior		137	133
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		167	172
Consumer loans | Nonaccrual loans | Home equity mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	0
Prior		6	6
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		6	6
Consumer loans | Accruing loans contractually past due 90 days or more
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	0
Prior		1	2
Revolving Loans		3	3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		4	5
Consumer loans | Accruing loans contractually past due 90 days or more | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	0
Prior		0	0
Revolving Loans		3	3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		3	3
Consumer loans | Accruing loans contractually past due 90 days or more | Consumer Portfolio Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		0	0
Two years prior to current year		0	0
Three years prior to current year		0	0
Four years prior to current year		0	0
Prior		1	2
Revolving Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		$ 1	$ 2

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at March 31, 2024 and December 31, 2023. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 15, "Variable Interest Entities," for additional information. March 31, 2024December 31, 2023(in millions)AssetsOther assets$21 $23 Total assets$21 $23 LiabilitiesInterest, taxes and other liabilities$28 $17 Total liabilities$28 $17