Fair value measurements - Additional Information (Detail) - USD ($) |
3 Months Ended | 12 Months Ended | |
|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Dec. 31, 2025 |
|
| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | |||
| Loans measured at fair value on nonrecurring basis | $ 314,000,000 | $ 524,000,000 | |
| Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves | (38,000,000) | (35,000,000) | |
| Level 2 | |||
| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | |||
| Loans measured at fair value on nonrecurring basis | 74,000,000 | 128,000,000 | |
| Level 3 | |||
| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | |||
| Loans measured at fair value on nonrecurring basis | 240,000,000 | 396,000,000 | |
| Level 3 | Residential Mortgage Loans | |||
| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | |||
| Capitalized servicing rights, valuation allowance | $ 0 | $ 0 | $ 0 |