Segment and geographic information - Major components of Income (loss) before income taxes in "Other" (Parenthetical) (Detail) ¥ in Millions	6 Months Ended
Sep. 30, 2021 JPY (¥)
Loss on legacy transactions	¥ 40,000
Nomura Research Institute, Ltd [Member]
Gain on the sale of the ordinary shares	¥ 36,249

The difference between the carrying value and the sale price of debt securities, not separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

Name:	us-gaap_GainLossOnSaleOfDebtInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration