Revenue from services provided to customers - Schedule of Disaggregation of Investment Banking Revenue (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Disaggregation Of Investment Banking Revenue [Abstract]
Equity underwriting and distribution fees	¥ 18,862	¥ 33,113	¥ 30,647
Debt underwriting and distribution fees	21,145	29,812	23,120
Financial advisory fees	53,946	64,240	37,760
Other fees	19,255	22,438	17,154
Total	¥ 113,208	¥ 149,603	¥ 108,681

Includes (1) underwriting revenue (the spread between the resale price received and the cost of the securities and related expenses) generated through the purchasing, distributing and reselling of new issues of securities (alternatively, could be a secondary offering of a large block of previously issued securities); and (2) fees earned for mergers, acquisitions, divestitures, restructurings, and other types of financial advisory services.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(b),(d))
-URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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