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Income and Expenses Relating to Life Insurance Operations - Life Insurance Premiums and Related Investment Income (Parenthetical) (Detail) - JPY (¥) ¥ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Net Investment Income [Line Items] |  |  |  |
Trading Securities, Unrealized Holding Gain (Loss) | ¥ 1,178 | ¥ (949) | ¥ 24,322 | ¥ (15,645)
Life insurance related investment income |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Trading Securities, Unrealized Holding Gain (Loss) | ¥ 55 | ¥ (1,222) | ¥ 18,115 | ¥ (9,465)

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