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Derivative financial instruments - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Jun. 30, 2025 | Dec. 31, 2024 | Jun. 30, 2024 | Dec. 31, 2023
Derivative [Line Items] |  |  |  |  |  |  |  |
Notional Amount | $ 31,100 |  | $ 31,100 |  |  | $ 36,184 |  |
Aggregate fair value of derivative financial instruments in asset position | 57 |  | 57 |  |  | 157 |  |
Collateral relating to net asset positions | 58 |  | 58 |  |  | 157 |  |
Cash Flow Hedges |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Equity, attributable to parent, before tax | 91 | $ 59 | 91 | $ 59 | $ 85 | (135) | $ (330) | $ (203)
Clearinghouse Credit Facilities |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Amount of initial margin posted | 237 |  | 237 |  |  | 257 |  |
Interest Income |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Change in cash flow hedges derivative instruments, fair value net | (22) | (102) | (108) | (288) |  |  |  |
Interest Rate Contracts | Not Designated as Hedging Instrument |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Notional Amount | 44,800 |  | 44,800 |  |  | 40,500 |  |
Foreign exchange and other option and futures contracts | Not Designated as Hedging Instrument |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Notional Amount | 2,000 |  | 2,000 |  |  | $ 1,600 |  |
Interest rate swap agreements |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Cash flow hedge reclassification before tax | (33) | $ (115) | (139) | $ (328) |  |  |  |
Interest rate swap agreements | Maturity Period 2026 |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Equity, attributable to parent, before tax | (6) |  | (6) |  |  |  |  |
Interest rate swap agreements | Maturity Period 2027 |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Equity, attributable to parent, before tax | 56 |  | 56 |  |  |  |  |
Interest rate swap agreements | Maturity Period 2028 |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Equity, attributable to parent, before tax | $ 29 |  | $ 29 |  |  |  |  |

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