Long-Duration Insurance Contracts Relating to Life Insurance Operations - Schedule of Balances of Policy Account (Detail) - Fixed Annuity And Annuitization Benefits - JPY (¥) ¥ in Millions	6 Months Ended	12 Months Ended
Sep. 30, 2024	Mar. 31, 2024
Policyholder Account Balance [Line Items]
Beginning balance	¥ 138,419	¥ 158,952
Transfer in	4,975	10,249
Surrenders and partial surrenders	(51)	(71)
Benefit payments and lump sum payments, etc	(14,502)	(31,179)
Policy charges	(109)	(229)
Transfer out	(209)	(290)
Interests	462	1,023
Others	(10)	(36)
Ending balance	¥ 128,975	¥ 138,419
Weighted average guaranteed interest rate (%)	0.70%	0.70%
Benefits in excess of policyholder account balances (Millions of yen)	¥ 0	¥ 1
Cash surrender value (Millions of yen)	¥ 123,132	¥ 132,411

Transfer from policyholder account balance to separate account.

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Transfer to policyholder account balance from separate account.

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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 interest expense for allocation to policyholder account balance.

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

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Amount of increase (decrease) in liability for policyholder account balance from change, classified as other.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of guaranteed benefit in excess of current account balance of policyholder account balance.

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Amount of decrease in liability for policyholder account balance from policy charge.

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Amount of decrease in liability for policyholder account balance from contract redemption.

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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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