Loans - Summary of Past Due Status of Loans (Detail) - USD ($) $ in Millions		Sep. 30, 2025	Dec. 31, 2024
Financing Receivable, Past Due [Line Items]
Loans, net	[1]	$ 64,503	$ 62,753
Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		41,870	41,051
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		6,241	6,612
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		25,802	25,426
Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		9,827	9,013
Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		22,633	21,702
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		21,994	21,035
Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		388	393
Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		175	195
Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net		76	79
Total Past Due 30 Days or More
Financing Receivable, Past Due [Line Items]
Loans, net		530	591
Total Past Due 30 Days or More | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		244	299
Total Past Due 30 Days or More | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		8	23
Total Past Due 30 Days or More | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		61	245
Total Past Due 30 Days or More | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		175	31
Total Past Due 30 Days or More | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		286	292
Total Past Due 30 Days or More | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		274	279
Total Past Due 30 Days or More | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		6	6
Total Past Due 30 Days or More | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		4	4
Total Past Due 30 Days or More | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net		2	3
30 - 89 Days
Financing Receivable, Past Due [Line Items]
Loans, net		359	278
30 - 89 Days | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		175	98
30 - 89 Days | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		0	4
30 - 89 Days | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		2	63
30 - 89 Days | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		173	31
30 - 89 Days | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		184	180
30 - 89 Days | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		179	174
30 - 89 Days | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		2	2
30 - 89 Days | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		2	2
30 - 89 Days | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net		1	2
90+ Days
Financing Receivable, Past Due [Line Items]
Loans, net		171	313
90+ Days | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		69	201
90+ Days | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		8	19
90+ Days | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		59	182
90+ Days | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		2	0
90+ Days | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		102	112
90+ Days | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		95	105
90+ Days | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		4	4
90+ Days | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		2	2
90+ Days | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net		1	1
Current
Financing Receivable, Past Due [Line Items]
Loans, net		63,973	62,162
Current | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net		41,626	40,752
Current | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net		6,233	6,589
Current | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net		25,741	25,181
Current | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net		9,652	8,982
Current | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net		22,347	21,410
Current | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		21,720	20,756
Current | Consumer loans | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans, net		382	387
Current | Consumer loans | Credit cards
Financing Receivable, Past Due [Line Items]
Loans, net		171	191
Current | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net		$ 74	$ 76

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at September 30, 2025 and December 31, 2024. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 15, "Variable Interest Entities," for additional information. September 30, 2025December 31, 2024(in millions)AssetsOther assets$7 $11 Total assets$7 $11 LiabilitiesInterest, taxes and other liabilities$14 $4 Total liabilities$14 $4