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Commitments and contingencies - Additional Information (Detail) - USD ($) $ in Millions | Jun. 30, 2026 | Dec. 31, 2025 | Dec. 17, 2025
--- | --- | --- | ---
Loss Contingencies [Line Items] |  |  |
Commitments to extend credit to commercial customers | $ 12,800 | $ 12,900 |
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program | 4,700 | 4,600 |
Loss contingency accrual | 0 | $ 22 |
Tricolor Holdings, LLC |  |  |
Loss Contingencies [Line Items] |  |  |
Fictitious loans |  |  | $ 683
Maximum |  |  |
Loss Contingencies [Line Items] |  |  |
Range of reasonably possible losses | $ 25 |  |

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