Revenue from services provided to customers - Schedule Of Disaggregation Of Investment Banking Revenue (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disaggregation Of Investment Banking Revenue [Abstract]
Equity underwriting and distribution	¥ 30,647	¥ 13,958	¥ 30,046
Bond underwriting and distribution	23,120	25,546	22,739
Financial advisory fees	37,760	41,646	33,195
Other	17,154	22,072	15,541
Total	¥ 108,681	¥ 103,222	¥ 101,521

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