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Derivative financial instruments - Information about Hedged Items Included in Consolidated Balance Sheet (Detail) - Designated as Hedging Instrument - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
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Carrying Amount | Long-term Debt |  |
Derivatives, Fair Value [Line Items] |  |
Hedged item | $ 6,092 | $ 5,184
Carrying Amount | Debt Securities, Available For Sale |  |
Derivatives, Fair Value [Line Items] |  |
Hedged item |  | 381
Estimated Fair Value | Long-term Debt |  |
Derivatives, Fair Value [Line Items] |  |
Hedged item | $ 5 | (155)
Estimated Fair Value | Debt Securities, Available For Sale |  |
Derivatives, Fair Value [Line Items] |  |
Hedged item |  | $ 0

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