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Derivative financial instruments - Information about Fair Values of Derivative Instruments in Consolidated Statement of Income (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivatives not designated as hedging instruments, derivatives | $ 22 | $ 9 | $ 38 | $ 18
Interest rate swap agreements | Fixed Rate Long-Term Borrowings | Designated as Hedging Instrument | Fair value hedges: |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, gain (loss), statement of income or comprehensive income [extensible enumeration] | Other costs of operations | Other costs of operations | Other costs of operations | Other costs of operations
Derivatives in fair value hedging relationships, derivative | $ (54) | $ 54 | $ (87) | $ 147
Derivatives in fair value hedging relationships, hedged item | 54 | (55) | 87 | (147)
Interest Rate Contracts |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivatives not designated as hedging instruments, derivatives | 17 | 7 | 27 | 12
Trading Account And Other Non Hedging Derivatives | Not Designated as Hedging Instrument |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivatives not designated as hedging instruments, derivatives | 18 | 7 | 26 |
Mortgage Banking Revenues | Not Designated as Hedging Instrument |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivatives not designated as hedging instruments, derivatives | 1 |  | 1 |
Foreign exchange and other option and futures contracts |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivatives not designated as hedging instruments, derivatives | $ 5 | $ 2 | $ 11 | $ 6

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