Severance Indemnities and Pension Plans (Aggregated Accumulated Benefit Obligations) (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2024	Mar. 31, 2023
Domestic, Japan \| Pension benefits and SIPs
Defined Benefit Plan Disclosure [Line Items]
Aggregated accumulated benefit obligations	¥ 1,425,853	¥ 1,521,419
Foreign offices and subsidiaries \| Pension benefits and other benefits
Defined Benefit Plan Disclosure [Line Items]
Aggregated accumulated benefit obligations	¥ 170,240	¥ 170,917

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
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

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