Revenue from services provided to customers - Schedule of Disaggregation of Asset Management Fees And Custody Fee (Detail) - JPY (¥) ¥ in Millions	6 Months Ended
Sep. 30, 2025	Sep. 30, 2024
Disaggregation Of Asset Management Fees And Custody Fee [Abstract]
Asset management fees	¥ 122,865	¥ 114,136
Administration fees	55,264	53,765
Custodial fees	17,213	16,280
Total	¥ 195,342	¥ 184,181

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