Loans - Summary of Past Due Status of Loans (Detail) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Loans, net	[1]	$ 59,797	$ 58,987
Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		40,305	39,957
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		7,071	7,087
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		16,047	15,724
Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Loans, net		10,522	10,725
Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		6,665	6,421
Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		19,492	19,030
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		18,825	18,341
Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		382	389
Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		189	199
Consumer loans | Consumer Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net		96	101
Past Due
Financing Receivable, Past Due [Line Items]
Loans, net		554	852
Past Due | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		279	561
Past Due | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		212	206
Past Due | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		4	4
Past Due | Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Loans, net		27	1
Past Due | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		36	350
Past Due | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		275	291
Past Due | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		254	265
Past Due | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		6	15
Past Due | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		5	6
Past Due | Consumer loans | Consumer Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net		10	5
30 - 89 Days
Financing Receivable, Past Due [Line Items]
Loans, net		243	543
30 - 89 Days | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		67	351
30 - 89 Days | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		7	0
30 - 89 Days | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		1	1
30 - 89 Days | Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Loans, net		23	0
30 - 89 Days | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		36	350
30 - 89 Days | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		176	192
30 - 89 Days | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		163	174
30 - 89 Days | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		3	12
30 - 89 Days | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		2	3
30 - 89 Days | Consumer loans | Consumer Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net		8	3
90+ Days
Financing Receivable, Past Due [Line Items]
Loans, net		311	309
90+ Days | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		212	210
90+ Days | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		205	206
90+ Days | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		3	3
90+ Days | Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Loans, net		4	1
90+ Days | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		0	0
90+ Days | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		99	99
90+ Days | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		91	91
90+ Days | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		3	3
90+ Days | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		3	3
90+ Days | Consumer loans | Consumer Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net		2	2
Current
Financing Receivable, Past Due [Line Items]
Loans, net		59,243	58,135
Current | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		40,026	39,396
Current | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		6,859	6,881
Current | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		16,043	15,720
Current | Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Loans, net		10,495	10,724
Current | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		6,629	6,071
Current | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		19,217	18,739
Current | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		18,571	18,076
Current | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		376	374
Current | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		184	193
Current | Consumer loans | Consumer Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net		$ 86	$ 96

[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