Revenue from services provided to customers - Schedule Of Disaggregation Of Investment Banking Revenue (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Investment Banking Revenue [Abstract]
Equity underwriting and distribution fees	¥ 33,113	¥ 30,647	¥ 13,958
Debt underwriting and distribution fees	29,812	23,120	25,546
Financial advisory fees	64,240	37,760	41,646
Other fees	22,438	17,154	22,072
Total	¥ 149,603	¥ 108,681	¥ 103,222

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 http://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