Loans - Credit Risk Profile of Commercial Loans (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 | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		170	3,217
One year prior to current year		2,887	1,705
Two years prior to current year		1,555	1,261
Three years prior to current year		1,279	807
Four years prior to current year		841	1,028
Prior		6,982	6,322
Revolving Loans		9,206	8,595
Revolving Loans Converted to Term Loans		63	54
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		22,983	22,989
Commercial loans | Investment grade | Real estate, including construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	327
One year prior to current year		324	100
Two years prior to current year		99	24
Three years prior to current year		23	187
Four years prior to current year		172	162
Prior		1,094	939
Revolving Loans		1	1
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		1,713	1,740
Commercial loans | Investment grade | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		73	732
One year prior to current year		533	304
Two years prior to current year		333	543
Three years prior to current year		562	95
Four years prior to current year		93	261
Prior		2,086	1,977
Revolving Loans		3,287	3,311
Revolving Loans Converted to Term Loans		63	54
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		7,030	7,277
Commercial loans | Investment grade | Global banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		82	1,947
One year prior to current year		1,868	1,109
Two years prior to current year		973	651
Three years prior to current year		651	149
Four years prior to current year		173	307
Prior		2,970	2,842
Revolving Loans		1,963	2,140
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		8,680	9,145
Commercial loans | Investment grade | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		15	211
One year prior to current year		162	192
Two years prior to current year		150	43
Three years prior to current year		43	376
Four years prior to current year		403	298
Prior		832	564
Revolving Loans		3,955	3,143
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		5,560	4,827
Commercial loans | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		328	1,439
One year prior to current year		1,705	2,163
Two years prior to current year		2,165	1,989
Three years prior to current year		2,038	581
Four years prior to current year		539	1,326
Prior		5,706	4,747
Revolving Loans		4,578	4,459
Revolving Loans Converted to Term Loans		263	264
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		17,322	16,968
Commercial loans | Non-investment grade | Real estate, including construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		164	593
One year prior to current year		658	1,186
Two years prior to current year		1,187	995
Three years prior to current year		1,017	168
Four years prior to current year		147	892
Prior		2,143	1,470
Revolving Loans		39	40
Revolving Loans Converted to Term Loans		3	3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		5,358	5,347
Commercial loans | Non-investment grade | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		164	538
One year prior to current year		751	844
Two years prior to current year		695	531
Three years prior to current year		745	136
Four years prior to current year		131	300
Prior		2,406	2,276
Revolving Loans		3,915	3,611
Revolving Loans Converted to Term Loans		210	211
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		9,017	8,447
Commercial loans | Non-investment grade | Global banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	308
One year prior to current year		294	44
Two years prior to current year		155	193
Three years prior to current year		110	2
Four years prior to current year		31	14
Prior		826	758
Revolving Loans		376	211
Revolving Loans Converted to Term Loans		50	50
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		1,842	1,580
Commercial loans | Non-investment grade | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Current year		0	0
One year prior to current year		2	89
Two years prior to current year		128	270
Three years prior to current year		166	275
Four years prior to current year		230	120
Prior		331	243
Revolving Loans		248	597
Revolving Loans Converted to Term Loans		0	0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Total		$ 1,105	$ 1,594

[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