Other Assets and Liabilities (Details of Other Assets and Liabilities) (Detail) - JPY (¥) ¥ in Millions |
Mar. 31, 2026 |
Mar. 31, 2025 |
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| Other assets: | ||||||||||||
| Receivables from brokers, dealers and customers for securities transactions | ¥ 2,190,046 | ¥ 2,730,316 | ||||||||||
| Other | 572,031 | 566,583 | ||||||||||
| Collateral pledged for derivative transactions | 2,305,536 | 1,666,564 | ||||||||||
| Margins provided for futures contracts | 303,332 | 228,386 | ||||||||||
| Other | 137,164 | 117,279 | ||||||||||
| Prepaid pension cost | 717,926 | 682,222 | ||||||||||
| Right-of-use assets | 483,068 | 474,361 | ||||||||||
| Security deposits | 71,005 | 76,648 | ||||||||||
| Loans held for sale | 162,289 | [1] | 391,519 | |||||||||
| Other | 1,139,694 | 1,300,551 | [2],[3] | |||||||||
| Total | ¥ 8,082,090 | ¥ 8,234,429 | ||||||||||
| Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] | Total | Total | ||||||||||
| Other liabilities: | ||||||||||||
| Payables to brokers, dealers and customers for securities transactions | ¥ 1,002,531 | ¥ 1,260,130 | ||||||||||
| Other | 1,136,689 | 611,344 | ||||||||||
| Guaranteed trust principal | [4] | 441,687 | 703,851 | |||||||||
| Lease liabilities | 521,941 | 502,997 | ||||||||||
| Collateral accepted for derivative transactions | 2,163,341 | 1,380,243 | ||||||||||
| Margins accepted for futures contracts | 57,053 | 29,725 | ||||||||||
| Unearned income | 86,294 | 93,491 | ||||||||||
| Other | 1,761,662 | 2,026,574 | [2] | |||||||||
| Total | ¥ 7,171,197 | ¥ 6,608,355 | ||||||||||
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- Definition Derivative Collateral Obligation To Return Cash Through Exchange No definition available.
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| X | ||||||||||
- Definition Derivative Collateral Right To Reclaim Cash Through Exchange No definition available.
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| X | ||||||||||
- Definition The liability of certain consolidated trust arrangements, which the reporting entity provides guarantees for the repayment of principal. No definition available.
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| X | ||||||||||
- Definition Prepaid pension cost. No definition available.
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| X | ||||||||||
- Definition Amount payable to other broker-dealer and clearing organization, including, but not limited to, security failed-to-receive, deposit received for security loaned, open transaction, and floor-brokerage payable. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of obligations incurred and payable classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of right to receive securities collateral under master netting arrangements that have not been offset against derivative liabilities. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Present value of lessee's discounted obligation for lease payments from operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of lessee's right to use underlying asset under operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Indicates line item in statement of financial position that includes operating lease right-of-use asset. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of assets classified as other. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of other miscellaneous assets. No definition available.
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- References No definition available.
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| X | ||||||||||
- Definition Amount of liabilities classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount due from parties in nontrade transactions, classified as other. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition The aggregate carrying amount, as of the balance sheets date, of obligations not otherwise itemized or categorized in the footnotes to the financial statements. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount receivable from broker-dealers and clearing organizations, including, but not limited to, securities failed-to-deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage receivables. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition The amount of an asset, typically cash, provided to a counterparty to provide certain assurance of performance by the entity pursuant to the terms of a written or oral agreement, such as a lease. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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