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Income and Expenses Relating to Life Insurance Operations - Gains or Losses Relating to Variable Annuity and Variable Life Insurance Contracts (Detail) - Variable Annuity and Variable Life Insurance Contracts - JPY (¥) ¥ in Millions	6 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Life insurance premiums and related investment income
Net realized and unrealized gains or losses from investment assets	¥ 21,706	¥ (2,704)
Net gains or losses from derivative contracts	(1,148)	(131)
Life insurance costs
Changes in the fair value of the policy liabilities and policy account balances	6,707	(15,980)
Insurance costs recognized for insurance and annuity payouts as a result of insured events	10,571	11,839
Changes in the fair value of the reinsurance contracts	1,071	(73)
Futures
Life insurance premiums and related investment income
Net gains or losses from derivative contracts	(1,106)	(141)
Foreign exchange contracts
Life insurance premiums and related investment income
Net gains or losses from derivative contracts	¥ (42)	¥ 10

X

- Definition

Amount of increase (decrease) in the fair value of reinsurance contracts in the income statement.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in the fair value of variable annuity and variable life insurance contracts.

+ References

No definition available.

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- Definition

Life Insurance Costs [Abstract]

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No definition available.

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- Definition

Life Insurance Premiums and Related Investment Income [Abstract]

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No definition available.

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- Definition

Amount, after effect of policies assumed or ceded, of expense related to provision for policyholder benefits and costs incurred for variable annuity and variable life insurance contracts.

+ References

No definition available.

+ Details

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- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-SubTopic 10
-Topic 825
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482881/825-10-55-10

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- Definition

Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-4

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