Summary of accounting policies - Additional information (Detail) ¥ in Millions	12 Months Ended
Mar. 31, 2022 JPY (¥) Segment	Mar. 31, 2021 JPY (¥)
Accounting Policy [Line Items]
Number of business segments \| Segment	3
Net receivables arising from unsettled securities transactions
Net payables arising from unsettled securities transactions	¥ 67,258	¥ 205,211
Minimum [Member]
Accounting Policy [Line Items]
Ownership percentage	20.00%
Maximum [Member]
Accounting Policy [Line Items]
Ownership percentage	50.00%
Limited partnership [Member] \| Minimum [Member]
Accounting Policy [Line Items]
Ownership percentage	3.00%

Accounting Policy [Line Items]

No definition available.

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- Definition

Net payables arising from unsettled securities transactions.

+ References

No definition available.

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- Definition

Net receivables arising from unsettled securities transactions reported within Receivables from other than customers

+ References

No definition available.

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8672-108599

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