Loans and allowance for loan losses - Additional Information (Detail) - USD ($) $ in Millions |
Jun. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Loans And Leases Receivable [Line Items] | ||
| Loans secured by residential real estate that were in the process of foreclosure | $ 186 | $ 182 |
| Percentage loans in the process of foreclosure, serviced by other entities, classified as government guaranteed | 59.00% | |
| Financing receivable, accrued interest, before allowance for credit loss | $ 625 | $ 627 |