Segment and geographic information - Major components of Income before income taxes in "Other" (Parenthetical) (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Gain (Loss) on Disposition of property, plant, and equipment	¥ 58,744	¥ (2,344)	¥ (2,670)
Affiliated Entity [Member] \| Land and Building [Member]
Segment Reporting Information [Line Items]
Gain (Loss) on Disposition of property, plant, and equipment	¥ 56,144

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Name:	us-gaap_GainLossOnSaleOfPropertyPlantEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration