Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 748	$ 720
Accruing Loans Contractually Past Due 90 Days or More	4	151
Nonaccrual Loans With No Allowance For Credit Losses	123	139
Residential mortgage loans carried at lower of cost or fair value of the collateral less cost to sell	99	106
Commercial loans
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	533	541
Accruing Loans Contractually Past Due 90 Days or More	0	147
Nonaccrual Loans With No Allowance For Credit Losses	50	54
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	257	261
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	2	21
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	273	280
Accruing Loans Contractually Past Due 90 Days or More	0	147
Nonaccrual Loans With No Allowance For Credit Losses	46	33
Commercial loans | Other commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	3
Accruing Loans Contractually Past Due 90 Days or More	0
Nonaccrual Loans With No Allowance For Credit Losses	2
Consumer loans
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	215	179
Accruing Loans Contractually Past Due 90 Days or More	4	4
Nonaccrual Loans With No Allowance For Credit Losses	73	85
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	206	173
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	67	80
Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	9	6
Accruing Loans Contractually Past Due 90 Days or More	4	4
Nonaccrual Loans With No Allowance For Credit Losses	$ 6	$ 5