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Commitments and contingencies - Additional Information (Detail) - USD ($) $ in Millions | Jun. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Loss Contingencies [Line Items] |  |
Commitments to extend credit to commercial customers | $ 12,600 | $ 12,700
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program | 4,300 | 4,200
Loss contingency accrual | 108 | $ 157
Minimum |  |
Loss Contingencies [Line Items] |  |
Range of reasonably possible losses | 0 |
Maximum |  |
Loss Contingencies [Line Items] |  |
Range of reasonably possible losses | $ 25 |

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