Obligations under Guarantees and Other Off-balance Sheet Instruments (Narrative) (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Guarantor Obligations [Line Items]
Amount of Obligations under Guarantees	¥ 86,790,000	¥ 81,144,000
Contractual maturities of guarantees mainly comprised of guarantees of housing loans, in years	5 years
Carrying amounts of the liabilities related to guarantees and similar instruments	¥ 1,329,100	1,242,232
Allowance for off-balance sheet instruments	¥ 62,262	58,314
Lending-related commitments which expire within one year, in approximate percentage	65.00%
Lending-related commitments which expire from one year to five years, in approximate percentage	32.00%
Lending-related commitments which expire after five years, in approximate percentage	3.00%
Portion syndicated out to third parties
Guarantor Obligations [Line Items]
Amount of Obligations under Guarantees	¥ 768,500	681,400
Options sold
Guarantor Obligations [Line Items]
Amount of Obligations under Guarantees	¥ 1,255,657	¥ 1,175,019

Amount of allowance for obligations under guarantees included in Other liabilities.

No definition available.

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- Definition

Approximate percentage which is the amount of commitments that expire after five years divided by total lending-related commitments.

+ References

No definition available.

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- Definition

Approximate percentage which is the amount of commitments that expire from one year to five years divided by total lending-related commitments.

+ References

No definition available.

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- Definition

Approximate percentage which is the amount of commitments that expire within one year divided by total lending-related commitments.

+ References

No definition available.

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- Definition

Number of contractual maturity years of guarantees which are mainly comprised of guarantees of housing loans.

+ References

No definition available.

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- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

+ Details

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- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

+ Details

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