v3.25.2
Severance Indemnities and Pension Plans (Amounts Recognized in OCI) (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Domestic, Japan | Pension benefits and SIPs    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial loss (gain) arising during the year ¥ (130,464) ¥ (585,393)
Prior service cost arising during the year 0 0
Losses (gains) due to amortization:    
Net actuarial loss (gain) 16,821 591
Prior service cost 282 1,974
Curtailment and settlement 13,754 13,659
Foreign currency translation adjustments 0 0
Total changes in Accumulated OCI (99,607) (569,169)
Foreign offices and subsidiaries | Pension benefits    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial loss (gain) arising during the year (1,570) 16,343
Prior service cost arising during the year (2,188) (608)
Losses (gains) due to amortization:    
Net actuarial loss (gain) (2,112) (1,362)
Prior service cost 1,328 945
Curtailment and settlement (15) (1,803)
Foreign currency translation adjustments 757 3,277
Total changes in Accumulated OCI (3,800) 16,792
Foreign offices and subsidiaries | Other benefits    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial loss (gain) arising during the year (490) 240
Prior service cost arising during the year 0 0
Losses (gains) due to amortization:    
Net actuarial loss (gain) 89 (1,191)
Prior service cost 449 426
Curtailment and settlement 0 0
Foreign currency translation adjustments (13) 162
Total changes in Accumulated OCI ¥ 35 ¥ (363)