Securitizations and Variable Interest Entities - Additional information (Detail) - JPY (¥) ¥ in Billions	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Variable Interest Entity [Line Items]
Cash proceeds from SPEs in new securitizations	¥ 187	¥ 382
Debt securities issued by SPEs with an initial fair value	2,574	1,867
Cash inflows from third parties on the sale of debt securities	1,833	1,412
Cumulative balance of financial assets transferred to SPEs	5,364	6,533
Retained interests	308	200
Interests held in SPEs	94	51
Outstanding collateral service agreements and written credit default swap agreements	¥ 2	¥ 2
Minimum [Member]
Variable Interest Entity [Line Items]
Percentage of changes in fair value based on adverse effect	10.00%	10.00%
Maximum [Member]
Variable Interest Entity [Line Items]
Percentage of changes in fair value based on adverse effect	20.00%	20.00%

Cash inflow (outflow) from SPEs on retained interests continuously held by entity.

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- Definition

Cumulative Balance of Financial Assets Transferred to Spes

+ References

No definition available.

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- Definition

Debt Securities Issued by Special Purpose Entities Initial Fair Value

+ References

No definition available.

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- Definition

Outstanding collateral service agreements and written credit default swap agreements

+ References

No definition available.

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- Definition

Percentage of changes in fair value based on adverse effect

+ References

No definition available.

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- Definition

The carrying amount (fair value) as of the balance sheet date of the transferor's interests in transferred financial assets (typically securitized receivables, generally not involved in the collection of principal) following transfer of significant portions of such financial instruments to other parties. Such interests could be ancillary cash flows and interest-only strips.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=64830801&loc=d3e107314-111719

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- Definition

The cash inflow associated with the sale of debt securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

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- Definition

The cash inflow from the securitization of loans held for investment. Securitization is the structured process whereby interests in loans and other receivables are packaged, underwritten, and sold in the form of asset-backed securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3574-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3521-108585

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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

No definition available.

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