Leases - Lessee: Supplemental Balance Sheet Information (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2025	Mar. 31, 2024
Operating And Finance Lease Supplemental Balance Sheet Information [Line Items]
Right-of-use asset (operating leases)	¥ 249,480	¥ 249,890
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Assets	Other Assets
Operating lease, Other Liabilities	¥ 251,860	¥ 252,344
Operating lease, Total lease liabilities	¥ 251,860	¥ 252,344
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Liabilities	Liabilities
Operating lease, Weighted average remaining lease term	12 years	11 years
Operating lease, Weighted average discount rate	1.70%	1.70%
Right-of-use asset (finance leases)	¥ 7,034	¥ 7,284
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Net Investment in Lease, before Allowance for Credit Loss	Net Investment in Lease, before Allowance for Credit Loss
Finance leases, Other Liabilities	¥ 7,479	¥ 7,877
Finance leases, Total lease liabilities	¥ 7,479	¥ 7,877
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities	Liabilities
Finance leases, Weighted average remaining lease term	35 years	35 years
Finance leases, Weighted average discount rate	2.00%	2.20%
Investment in Operating Leases
Operating And Finance Lease Supplemental Balance Sheet Information [Line Items]
Right-of-use asset (operating leases)	¥ 68,883	¥ 82,674
Right-of-use asset (finance leases)	4,634	4,685
Property under Facility Operations
Operating And Finance Lease Supplemental Balance Sheet Information [Line Items]
Right-of-use asset (operating leases)	99,201	72,284
Right-of-use asset (finance leases)	1,863	2,306
Office Facilities
Operating And Finance Lease Supplemental Balance Sheet Information [Line Items]
Right-of-use asset (operating leases)	81,396	94,932
Right-of-use asset (finance leases)	¥ 537	¥ 293

Present value of lessee's discounted obligation for lease payments from finance lease

No definition available.

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- Definition

Finance leases, Total lease liabilities.

+ References

No definition available.

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- References

No definition available.

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- Definition

Present value of lessee's discounted obligation for lease payments from operating lease

+ References

No definition available.

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Data Type:	xbrli:monetaryItemType
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- Definition

Indicates line item in statement of financial position that includes finance lease liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-2

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- Definition

Amount, after accumulated amortization, of right-of-use asset from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

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- Definition

Indicates line item in statement of financial position that includes finance lease right-of-use asset.

+ References

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- Definition

Weighted average discount rate for finance lease calculated at point in time.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 53
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479589/842-20-55-53

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 4
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

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- Definition

Weighted average remaining lease term for finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 53
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479589/842-20-55-53

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (g)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

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- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

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- Definition

Indicates line item in statement of financial position that includes operating lease liability.

+ References

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- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

+ Details

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Balance Type:	debit
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- Definition

Indicates line item in statement of financial position that includes operating lease right-of-use asset.

+ References

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- Definition

Weighted average discount rate for operating lease calculated at point in time.

+ References

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- Definition

Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 53
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479589/842-20-55-53

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (g)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

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