Loans - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	$ 61,586		$ 59,894
Interest income that was recorded on nonaccrual loans and included in interest income during the period	0	$ 0
90+ Days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	306		229
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	41,234		39,344
Collateral-dependent loans	544		513
Loans modified	169	14
Additional commitments for loans modified	106		116
Commercial loans | 90+ Days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	186		121
Loans modified, subsequently default	0	0
Commercial loans | Business and corporate banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	30,635		28,305
Loans modified	152	14
Commercial loans | Business and corporate banking | Reclassification
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net			3,200
Commercial loans | Business and corporate banking | 90+ Days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	81		15
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	20,352		20,550
Loans modified	0	$ 0
Consumer loans | 90+ Days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	120		108
Consumer loans | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	19,609		19,789
Collateral-dependent loans	269		256
Consumer loans | Residential mortgages | 90+ Days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	$ 112		$ 100