Commitments, Guarantees, and Contingent Liabilities (Summary of Potential Future Payments, Book Value Recorded as Guarantee Liabilities of Guarantee Contracts Outstanding and Maturity of Longest Guarantee Contracts) (Detail) - JPY (¥) ¥ in Millions |
6 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Mar. 31, 2026 |
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| Guarantor Obligations [Line Items] | ||||
| Potential future payment | ¥ 1,247,722 | ¥ 1,247,252 | ||
| Book value of guarantee liabilities | 20,326 | 19,713 | ||
| Transferred loans | ||||
| Guarantor Obligations [Line Items] | ||||
| Potential future payment | 609,236 | 609,536 | ||
| Book value of guarantee liabilities | ¥ 14,183 | ¥ 13,760 | ||
| Maturity of the longest contract (Years) | 2067 | 2062 | ||
| Real estate loans | ||||
| Guarantor Obligations [Line Items] | ||||
| Potential future payment | [1] | ¥ 1,988 | ¥ 6,524 | |
| Book value of guarantee liabilities | [1] | ¥ 0 | ¥ 0 | |
| Maturity of the longest contract (Years) | [1] | 2045 | Undetermined | |
| Other | ||||
| Guarantor Obligations [Line Items] | ||||
| Potential future payment | ¥ 19,318 | ¥ 18,225 | ||
| Book value of guarantee liabilities | ¥ 0 | ¥ 0 | ||
| Maturity of the longest contract (Years) | 2055 | 2043 | ||
| Corporate loans | ||||
| Guarantor Obligations [Line Items] | ||||
| Potential future payment | ¥ 617,180 | ¥ 612,967 | ||
| Book value of guarantee liabilities | ¥ 6,143 | ¥ 5,953 | ||
| Maturity of the longest contract (Years) | 2033 | 2033 | ||
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