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Loans and allowance for loan losses - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024 | Dec. 31, 2024
Loans And Leases Receivable [Line Items] |  |  |  |  |
Amount of foreclosed residential real estate property held | $ 30 |  | $ 30 |  | $ 35
Loans secured by residential real estate that were in the process of foreclosure | $ 194 |  | $ 194 |  | 173
Percentage loans in the process of foreclosure, serviced by other entities, classified as government guaranteed | 46.00% |  | 46.00% |  |
Financing receivable, accrued interest, before allowance for credit loss | $ 617 |  | $ 617 |  | 628
Commercial and industrial |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Weighted-average remaining term | 7 months 6 days | 8 months 12 days | 9 months 18 days | 9 months 18 days |
Commercial and industrial | Asset Pledged as Collateral without Right |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Financing receivable, before allowance for credit loss | $ 20,900 |  | $ 20,900 |  |
Commercial and industrial | Asset Pledged as Collateral without Right | FHLBs Facility |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Pledged financial instruments |  |  |  |  | 20,700
Commercial Real Estate |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Weighted-average remaining term |  |  | 9 months 18 days |  |
Commercial Real Estate | Asset Pledged as Collateral without Right |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Financing receivable, before allowance for credit loss | $ 13,600 |  | $ 13,600 |  |
Commercial Real Estate | Asset Pledged as Collateral without Right | FHLBs Facility |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Pledged financial instruments |  |  |  |  | 14,600
Residential Real Estate |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Weighted-average remaining term | 9 years 2 months 12 days | 8 years 10 months 24 days | 9 years 8 months 12 days | 10 years 2 months 12 days |
Residential Real Estate | Asset Pledged as Collateral without Right |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Financing receivable, before allowance for credit loss | $ 19,000 |  | $ 19,000 |  |
Residential Real Estate | Asset Pledged as Collateral without Right | FHLBs Facility |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Pledged financial instruments |  |  |  |  | 18,600
Residential builder and developer |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Weighted-average remaining term |  | 7 months 6 days |  | 9 months 18 days |
Home equity lines and loans | Consumer | Asset Pledged as Collateral without Right |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Financing receivable, before allowance for credit loss | 2,800 |  | 2,800 |  |
Home equity lines and loans | Consumer | Asset Pledged as Collateral without Right | FHLBs Facility |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Pledged financial instruments |  |  |  |  | 2,700
Other | Consumer | Asset Pledged as Collateral without Right |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Financing receivable, before allowance for credit loss | $ 13,200 |  | $ 13,200 |  |
Other | Consumer | Asset Pledged as Collateral without Right | FHLBs Facility |  |  |  |  |
Loans And Leases Receivable [Line Items] |  |  |  |  |
Pledged financial instruments |  |  |  |  | $ 13,100

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