Collateralized transactions - Schedule of securities received as collateral (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2017	Mar. 31, 2017
Collateralized transactions
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	¥ 48,003	¥ 45,821
The portion of the above that has been sold (reported within Trading liabilities in the consolidated balance sheets) or repledged	¥ 41,328	¥ 39,119

Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

Name:	us-gaap_FairValueOfSecuritiesReceivedAsCollateralThatHaveBeenResoldOrRepledged
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant