Fair value measurements - Additional information (Detail) - JPY (¥) ¥ in Billions	Sep. 30, 2022	Mar. 31, 2022
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Differences between the fair value of the aggregate unpaid principal balance (which is contractually principally protected) of loans and receivables, more (less) than the principal balance of such loans and receivables	¥ 347	¥ 267
Differences between the fair value of the aggregate unpaid principal balance (which is contractually principally protected) of long-term borrowings more (less) than the principal balance of such long-term borrowings	487	212
The amount of loans and receivables with fair value options that are past due for 90 days or more	¥ 329	¥ 278
Concentrations of credit risk, percentage	16.00%	16.00%
American Century Companies, Inc. [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Percentage of economic interest	39.87%	39.21%

Concentration risk percentage.

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Economic Interest, Percentage

+ References

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- References

No definition available.

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This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of loans and long-term receivables (other than securities categorized as trading, available-for-sale or held-to-maturity) that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(1)
-URI https://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612

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- Definition

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of long-term debt instruments that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(2)
-URI https://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612

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- Definition

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are 90 days or more past due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI https://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612

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