Revenue from services provided to customers - Schedule of disaggregation of asset management fees and custody fee (Detail) - JPY (¥) ¥ in Millions	3 Months Ended	6 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Asset Management Fees And Custody Fee [Abstract]
Asset management fees	¥ 41,994	¥ 37,598	¥ 82,579	¥ 72,836
Administration fees	20,361	15,684	39,266	30,208
Custodial fees	4,838	4,135	9,392	8,029
Total	¥ 67,193	¥ 57,417	¥ 131,237	¥ 111,073

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.

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