Other assets-Other / Other liabilities - Schedule of Other assets-Other and Other liabilities (Parenthetical) (Detail) - JPY (¥) ¥ in Millions		6 Months Ended
Apr. 01, 2020	Sep. 30, 2020
Other Assets Other and Other Liabilities [Line Items]
Business acquisition percentage of voting interests acquired	100.00%	100.00%
Business acquisition name of acquired entity	Greentech Capital, LLC	Greentech Capital, LLC
Equity securities without readily determinable fair value		¥ 65,365

Other Assets Other and Other Liabilities [Line Items]

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- Definition

Name of the acquired entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117539-209714

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