Collateralized transactions - Fair Value of Securities Received as Collateral Available to Sell or Repledge (Detail) (JPY ¥) In Billions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Financial instruments received as collateral, borrowed with collateral and without collateral [Line items]
The fair value of securities received as collateral, securities borrowed as collateral and securities borrowed without collateral where Nomura is permitted by contract or custom to sell or repledge the securities	¥ 35,281	¥ 32,075
The portion of the above that has been sold (reported within Trading liabilities in the consolidated balance sheets) or repledged	¥ 28,488	¥ 23,895

This is the fair value as of the date of each statement of financial position presented of the collateral that is permitted, by contact or custom, to be sold or re-pledged.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 17

-Subparagraph a(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant