Severance Indemnities and Pension Plans (Summary for Plans with Accumulated Benefit Obligations in Excess of Plan Assets) (Detail) - JPY (¥) ¥ in Millions	Mar. 31, 2024	Mar. 31, 2023
Domestic, Japan \| Pension benefits and SIPs
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets:
Projected benefit obligations	¥ 24,655	¥ 24,918
Accumulated benefit obligations	24,655	24,918
Fair value of plan assets	7,771	7,315
Foreign offices and subsidiaries \| Pension benefits and other benefits
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets:
Projected benefit obligations	93,353	81,128
Accumulated benefit obligations	66,804	62,308
Fair value of plan assets	¥ 9,708	¥ 12,995

Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-3

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