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Accumulated Other Comprehensive Income (Loss) (Changes in Components of Accumulated Other Comprehensive Income (Loss)) (Parenthetical) (Detail) - JPY (¥) ¥ in Millions | 6 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024
Net unrealized gains (losses) on investment in securities |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Net unrealized gains (losses), tax | ¥ 33,944 | ¥ 21,373
Reclassification adjustment included in net income, tax | 1,767 | 1,380
Net unrealized gains (losses) on investments | (186) | (39)
Net unrealized gains (losses) on investments, net of tax | 28 | 15
Impact of changes in policy liability discount rate |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Net unrealized gains (losses), tax | (108,460) | 92
Debt valuation adjustments |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Net unrealized gains (losses), tax | (78) | 28
Reclassification adjustment included in net income, tax | 1 | 1
Defined benefit pension plans |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Net unrealized gains (losses), tax | (2,580) | 178
Reclassification adjustment included in net income, tax | 69 | 70
Foreign currency translation adjustments |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Net unrealized gains (losses), tax | 14,315 | (2,971)
Reclassification adjustment included in net income, tax | 3,134 | (2,332)
Net unrealized gains (losses) on derivative instruments |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Net unrealized gains (losses), tax | (13) | 2,552
Reclassification adjustment included in net income, tax | ¥ 1,417 | ¥ (1,397)

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