Loans - Summary of Past Due Status of Loans (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Financing Receivable, Past Due [Line Items]
Loans, net	$ 59,894	$ 62,753
Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net	39,344	41,051
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net	4,662	6,612
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net	25,082	25,426
Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net	9,600	9,013
Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net	20,550	21,702
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net	19,789	21,035
Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net	761	667
Total Past Due 30 Days or More
Financing Receivable, Past Due [Line Items]
Loans, net	693	591
Total Past Due 30 Days or More | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net	401	299
Total Past Due 30 Days or More | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net	106	23
Total Past Due 30 Days or More | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net	254	245
Total Past Due 30 Days or More | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net	41	31
Total Past Due 30 Days or More | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net	292	292
Total Past Due 30 Days or More | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net	278	279
Total Past Due 30 Days or More | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net	14	13
30 - 89 Days
Financing Receivable, Past Due [Line Items]
Loans, net	464	278
30 - 89 Days | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net	280	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	239	63
30 - 89 Days | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net	41	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	178	174
30 - 89 Days | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net	6	6
90+ Days
Financing Receivable, Past Due [Line Items]
Loans, net	229	313
90+ Days | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net	121	201
90+ Days | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net	106	19
90+ Days | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net	15	182
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	108	112
90+ Days | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net	100	105
90+ Days | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net	8	7
Current
Financing Receivable, Past Due [Line Items]
Loans, net	59,201	62,162
Current | Commercial loans
Financing Receivable, Past Due [Line Items]
Loans, net	38,943	40,752
Current | Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Loans, net	4,556	6,589
Current | Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans, net	24,828	25,181
Current | Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Loans, net	9,559	8,982
Current | Consumer loans
Financing Receivable, Past Due [Line Items]
Loans, net	20,258	21,410
Current | Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans, net	19,511	20,756
Current | Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Loans, net	$ 747	$ 654