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Fair value measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - USD ($) | Sep. 30, 2025 | Dec. 31, 2024
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Level 3 | Measurement Input, Commitment Expiration |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held-for-sale measurement input (as a percent) | 0.26 | 0.06
Recurring | Fair Value Measurements |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Trading account | $ 95,000,000 | $ 101,000,000
Investment securities available for sale: | 23,163,000,000 | 18,849,000,000
Equity securities | 258,000,000 | 235,000,000
Real estate loans held for sale | 605,000,000 | 521,000,000
Other assets | 253,000,000 | 255,000,000
Total assets | 24,374,000,000 | 19,961,000,000
Other liabilities | 480,000,000 | 822,000,000
Total liabilities | 480,000,000 | 822,000,000
Recurring | Fair Value Measurements | U.S. Treasury |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 6,620,000,000 | 7,931,000,000
Recurring | Fair Value Measurements | Commercial |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 4,861,000,000 | 3,702,000,000
Recurring | Fair Value Measurements | Residential |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 11,680,000,000 | 7,214,000,000
Recurring | Fair Value Measurements | Other |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 2,000,000 | 2,000,000
Recurring | Level 1 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Trading account | 95,000,000 | 101,000,000
Investment securities available for sale: | 0 | 0
Equity securities | 258,000,000 | 235,000,000
Real estate loans held for sale | 0 | 0
Other assets | 0 | 0
Total assets | 353,000,000 | 336,000,000
Other liabilities | 0 | 0
Total liabilities | 0 | 0
Recurring | Level 1 | U.S. Treasury |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 0 | 0
Recurring | Level 1 | Commercial |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 0 | 0
Recurring | Level 1 | Residential |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 0 | 0
Recurring | Level 1 | Other |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 0 | 0
Recurring | Level 2 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Trading account | 0 | 0
Investment securities available for sale: | 23,163,000,000 | 18,849,000,000
Equity securities | 0 | 0
Real estate loans held for sale | 605,000,000 | 521,000,000
Other assets | 248,000,000 | 251,000,000
Total assets | 24,016,000,000 | 19,621,000,000
Other liabilities | 480,000,000 | 790,000,000
Total liabilities | 480,000,000 | 790,000,000
Recurring | Level 2 | U.S. Treasury |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 6,620,000,000 | 7,931,000,000
Recurring | Level 2 | Commercial |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 4,861,000,000 | 3,702,000,000
Recurring | Level 2 | Residential |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 11,680,000,000 | 7,214,000,000
Recurring | Level 2 | Other |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 2,000,000 | 2,000,000
Recurring | Level 3 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Trading account | 0 | 0
Investment securities available for sale: | 0 | 0
Equity securities | 0 | 0
Real estate loans held for sale | 0 | 0
Other assets | 5,000,000 | 4,000,000
Total assets | 5,000,000 | 4,000,000
Other liabilities | 0 | 32,000,000
Total liabilities | 0 | 32,000,000
Recurring | Level 3 | U.S. Treasury |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 0 | 0
Recurring | Level 3 | Commercial |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 0 | 0
Recurring | Level 3 | Residential |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | 0 | 0
Recurring | Level 3 | Other |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Investment securities available for sale: | $ 0 | $ 0

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