Severance Indemnities and Pension Plans (Aggregated Accumulated Benefit Obligations) (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2023	Mar. 31, 2022
Domestic, Japan \| Pension benefits and SIPs
Defined Benefit Plan Disclosure [Line Items]
Aggregated accumulated benefit obligations	¥ 1,521,419	¥ 1,663,543
Foreign offices and subsidiaries \| Pension benefits and other benefits
Defined Benefit Plan Disclosure [Line Items]
Aggregated accumulated benefit obligations	¥ 170,917	¥ 596,153

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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