Deposits received at banks - Additional Information (Detail) - JPY (¥) ¥ in Billions	Mar. 31, 2026	Mar. 31, 2025
Statistical Disclosure for Banks [Abstract]
Amounts of uninsured time deposit liabilities	¥ 2,530	¥ 1,918

Amount of uninsured deposit liability.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph e
-Publisher SEC

Name:	us-gaap_DepositLiabilityUninsured
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant