v3.26.1
Pension and Other Employee Benefit Plans (Components of Net Periodic Costs of Severance Indemnities and Pension Plans) (Detail) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Defined Benefit Plan Disclosure [Line Items]      
Service cost-benefits earned during the fiscal year ¥ 18,192 ¥ 21,288 ¥ 28,936
Interest costs on projected benefit obligations 19,280 14,459 9,982
Expected return on plan assets (32,633) (31,835) (34,565)
Amortization of prior service cost (benefits) (5,682) (5,553) (4,890)
Amortization of net actuarial loss (gain) (32,420) (38,339) (29,045)
Special termination benefits 835 971 1,244
Loss (gain) on settlement 0 0 2,210
Other 2,118 2,004 3,179
Net periodic benefit cost ¥ (30,310) ¥ (37,005) ¥ (22,948)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Interest Expense, Deposits    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Investment Income, Interest