Revenue from services provided to customers - Schedule Of Disaggregation Of Asset Management Fees And Custody Fee (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disaggregation Of Asset Management Fees And Custody Fee [Abstract]
Asset management fees	¥ 150,218	¥ 159,494	¥ 168,695
Administration fees	63,215	62,619	60,983
Custodial fees	16,614	16,089	15,841
Total	¥ 230,047	¥ 238,202	¥ 245,519

Revenue recognized in the period for (1) performance(incentive) fees based on the investment results achieved for management of certain institutional accounts and hedge funds, (2) schedule-based fees earned for management of mutual funds and closed-end funds, based either on average daily net assets or on a combination of the average daily net assets and gross income, and (3) other investment management and advisory fees, (4) fees charged for services related to holding, advising, and managing customer investment assets.

No definition available.

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