Income and Expenses Relating to Life Insurance Operations - Gains or Losses Relating to Variable Annuity and Variable Life Insurance Contracts (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Life insurance premiums and related investment income
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Unrealized Gains Loss On Derivative Instruments	Unrealized Gains Loss On Derivative Instruments	Unrealized Gains Loss On Derivative Instruments
Variable Annuity and Variable Life Insurance Contracts
Life insurance premiums and related investment income
Net realized and unrealized gains or losses from investment assets	¥ (3,496)	¥ 40,821	¥ (2,312)
Net gains or losses from derivative contracts	(372)	(3,568)	(1,360)
Life insurance costs
Changes in the fair value of the policy liabilities and policy account balances	(30,998)	3,208	(35,097)
Insurance costs recognized for insurance and annuity payouts as a result of insured events	23,706	26,997	28,754
Changes in the fair value of the reinsurance contracts	200	1,890	538
Variable Annuity and Variable Life Insurance Contracts \| Futures
Life insurance premiums and related investment income
Net gains or losses from derivative contracts	(262)	(3,046)	(855)
Variable Annuity and Variable Life Insurance Contracts \| Foreign exchange contracts
Life insurance premiums and related investment income
Net gains or losses from derivative contracts	¥ (110)	¥ (522)	¥ (505)

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

No definition available.

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- Definition

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

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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.

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No definition available.

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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

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- Definition

Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative.

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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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