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Investment Securities - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2024 USD ($) security | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Summary of Investment Holdings [Line Items] |  |  |
Gross realized gains (loss) on sale of investment securities |  | $ 0 | $ 0
Number of securities | security | 3,820 |  |
Unrealized losses on individual debt securities | $ 1,500,000,000 |  |
Cost method equity securities | 772,000,000 |  |
Allowance for credit losses | 0 | 0 |
Investment securities, pledged as collateral for public deposits | 6,200,000,000 | 8,200,000,000 |
Debt Securities, Available-for-Sale, Realized Gain | 27,000,000 |  |
Debt Securities, Available-for-Sale, Realized Loss | 15,000,000 |  |
Repurchase Transactions |  |  |
Summary of Investment Holdings [Line Items] |  |  |
Investment securities, pledged as collateral for public deposits | $ 71,000,000 | $ 393,000,000 |

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