Securitizations and Variable Interest Entities - Additional Information (Detail) (JPY ¥) In Billions, unless otherwise specified	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Variable Interest Entity [Line Items]
Proceeds received from new securitizations	¥ 407	¥ 349
Debt securities issued by special purpose entities initial fair value	1,783	1,336
Cash inflows from third parties on the sale of debt securities	951	723
Cumulative balance of financial assets to SPEs	4,109	3,782
Retained interest	300	165
Interests held in SPEs	26	14
Outstanding collateral service agreements or written credit default swap agreements	¥ 18	¥ 27
Minimum [Member]
Variable Interest Entity [Line Items]
Percentage of changes in fair value based on adverse effect	10.00%
Maximum [Member]
Variable Interest Entity [Line Items]
Percentage of changes in fair value based on adverse effect	20.00%

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+ Details

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=6871852&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=6943989&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

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 16

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 18

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 15

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- 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+ Details