Securitizations and Variable Interest Entities - Type and carrying value of financial assets (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2018	Mar. 31, 2018
Liabilities [Abstract]
Long-term borrowings	¥ 7,694,241	¥ 7,382,507
Transferred to SPEs [Member]
Trading assets
Equities		1,000
Debt securities	5,000	20,000
CMBS and RMBS
Loans	14,000	1,000
Total	19,000	22,000
Liabilities [Abstract]
Long-term borrowings	¥ 19,000	¥ 21,000

Loans included within Trading assets, carrying value

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- Definition

Trading Assets And Liabilities Textual [Abstract]

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- Definition

Trading Assets and Long-term Loans Receivable

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No definition available.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Topic 210
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

+ References

No definition available.

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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- Definition

Fair value of investments in trading equity securities and other forms of trading securities that provide ownership interests.

+ References

No definition available.

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