Financing receivables - Additional information (Detail) - JPY (¥) ¥ in Millions	Sep. 30, 2022	Mar. 31, 2022
Corporate Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired financing receivable with related allowance unpaid principal balance	¥ 70,103	¥ 62,289

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant