Long-Duration Insurance Contracts Relating to Life Insurance Operations - Schedule of Single-Payment Whole Life Insurance (Detail) - Whole Life Insurance [Member] - JPY (¥) ¥ in Millions	6 Months Ended	12 Months Ended
Sep. 30, 2025	Mar. 31, 2025
Liability for Future Policy Benefit, Activity [Line Items]
Beginning balance	¥ 134,572	¥ 0
New contract	99,129	136,863
Surrenders and partial surrenders	(284)	(66)
Benefit payments and lump sum payments, etc.	(332)	(49)
Policy charges	(832)	(188)
Interests	4,705	1,072
Effect of changes in foreign exchange rate	1,379	(3,060)
Ending balance	¥ 238,337	¥ 134,572
Weighted average guaranteed interest rate (%)	5.10%	3.90%
Benefits in excess of policy account balances (Millions of yen)	¥ 0	¥ 0
Cash surrender value (Millions of yen)	¥ 230,259	¥ 127,659

Policyholder net exchange rate fluctuations.

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Amount of cash to be paid to policyholder upon termination and surrender of long-duration contract issued by insurance entity.

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Amount of cash outflow to policyholder account balance from benefit payment.

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Weighted-average crediting rate for liability for policyholder account balance, calculated at a point in time.

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Amount due to policyholder. Includes, but is not limited to, unpaid policy dividend, retrospective refund, and undistributed earnings on participating business. Excludes future policy benefit and claim expense.

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