Derivative instruments and hedging activities - Net Investment Hedges (Detail) (JPY ¥) In Billions, unless otherwise specified	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Derivative [Line Items]
Other comprehensive income (loss)	¥ (29)	¥ 3	¥ 17
Long-term borrowings [Member]
Derivative [Line Items]
Other comprehensive income (loss)	(15)	4	17
Foreign exchange contracts [Member]
Derivative [Line Items]
Other comprehensive income (loss)	¥ (14)	¥ (1)	¥ 0

Gain (Loss), net of tax, included in other comprehensive income derived from derivatives designated as hedges of net investment in foreign operations.

No definition available.

Name:	nmr_AmountOfOtherComprehensiveIncomeDerivedFromDerivativesDesignatedAsHedgesOfNetInvestmentInForeignOperations
Namespace Prefix:	nmr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration