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Investment in Securities (Summary of Contractual Maturities of Available-for-Sale Debt Securities) (Detail) - JPY (¥) ¥ in Millions | Mar. 31, 2024 | Mar. 31, 2023
--- | --- | ---
Available-for-sale debt securities, amortized cost |  |
Due within one year | ¥ 114,190 |
Due after one to five years | 347,324 |
Due after five to ten years | 394,644 |
Due after ten years | 2,159,782 |
Available-for-sale debt securities, Amortized cost | 3,015,940 | ¥ 2,488,858
Available-for-sale debt securities, fair value |  |
Due within one year | 114,074 |
Due after one to five years | 351,997 |
Due after five to ten years | 403,268 |
Due after ten years | 1,796,139 |
Available-for-sale debt securities | ¥ 2,665,478 | ¥ 2,234,608

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