v3.26.1
Severance Indemnities and Pension Plans (Amounts Recognized in OCI) (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Domestic, Japan | Pension benefits and SIPs    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial gain arising during the year ¥ (355,708) ¥ (130,464)
Prior service cost arising during the year (244) 0
Losses (gains) due to amortization:    
Net actuarial loss (gain) 30,905 16,821
Prior service cost (147) 282
Curtailment and settlement 15,807 13,754
Foreign currency translation adjustments 0 0
Total changes in Accumulated OCI (309,387) (99,607)
Foreign offices and subsidiaries | Pension benefits    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial gain arising during the year (305) (1,570)
Prior service cost arising during the year 0 (2,188)
Losses (gains) due to amortization:    
Net actuarial loss (gain) (2,243) (2,112)
Prior service cost 420 1,328
Curtailment and settlement (2,875) (15)
Foreign currency translation adjustments 2,439 757
Total changes in Accumulated OCI (2,564) (3,800)
Foreign offices and subsidiaries | Other benefits    
Defined Benefit Plan Disclosure [Line Items]    
Net actuarial gain arising during the year (1,011) (490)
Prior service cost arising during the year 0 0
Losses (gains) due to amortization:    
Net actuarial loss (gain) (23) 89
Prior service cost 444 449
Curtailment and settlement 0 0
Foreign currency translation adjustments 34 (13)
Total changes in Accumulated OCI ¥ (556) ¥ 35