Income taxes - Schedule of income taxes paid (Detail) ¥ in Millions	12 Months Ended
Mar. 31, 2026 JPY (¥)
Income Taxes Paid [Line Items]
Income taxes paid	¥ 118,852
Domestic National Tax [Member]
Income Taxes Paid [Line Items]
Income taxes paid	74,617
Domestic Local Tax [Member]
Income Taxes Paid [Line Items]
Income taxes paid	21,161
Foreign Tax [Member]
Income Taxes Paid [Line Items]
Income taxes paid	23,074
Tokyo [Member] \| Domestic Local Tax [Member]
Income Taxes Paid [Line Items]
Income taxes paid	13,182
Others [Member] \| Domestic Local Tax [Member]
Income Taxes Paid [Line Items]
Income taxes paid	¥ 7,979

Amount, before refund, of cash paid to foreign, federal, state, and local jurisdictions as income tax.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-2A

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 23
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-23

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-22

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
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-URI https://asc.fasb.org/1943274/2147482740/230-10-45-25

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
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-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-2

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