v3.25.2
Severance Indemnities and Pension Plans (Summary of Assumptions Used in Computation) (Detail)
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Domestic, Japan | Pension benefits and SIPs      
Defined Benefit Plan Disclosure [Line Items]      
Discount rates in determining expense 1.70% 1.36% 0.86%
Discount rates in determining benefit obligation 2.89% 1.70% 1.36%
Rates of increase in future compensation level for determining expense 3.49% 3.47% 3.46%
Rates of increase in future compensation level for determining benefit obligation 3.91% 3.49% 3.47%
Expected rates of return on plan assets 2.89% 2.97% 2.93%
Cash balance crediting rate for determining expense 2.46% 2.46% 2.46%
Cash balance crediting rate for determining benefit obligation 2.53% 2.46% 2.46%
Foreign offices and subsidiaries | Pension benefits      
Defined Benefit Plan Disclosure [Line Items]      
Discount rates in determining expense 5.06% 4.74% 2.51%
Discount rates in determining benefit obligation 5.22% 5.06% 4.76%
Rates of increase in future compensation level for determining expense 5.50% 5.09% 5.04%
Rates of increase in future compensation level for determining benefit obligation 5.44% 5.50% 5.09%
Expected rates of return on plan assets 5.93% 4.98% 4.86%
Cash balance crediting rate for determining expense 4.38% 3.72% 1.94%
Cash balance crediting rate for determining benefit obligation 4.59% 4.38% 3.72%
Foreign offices and subsidiaries | Other benefits      
Defined Benefit Plan Disclosure [Line Items]      
Discount rates in determining expense 5.00% 4.59% 2.21%
Discount rates in determining benefit obligation 5.26% 5.06% 4.68%
Rates of increase in future compensation level for determining expense 0.00% 0.00% 0.00%
Rates of increase in future compensation level for determining benefit obligation 0.00% 0.00% 0.00%
Expected rates of return on plan assets 7.00% 6.25% 5.50%
Cash balance crediting rate for determining expense 0.00% 0.00% 0.00%
Cash balance crediting rate for determining benefit obligation 0.00% 0.00% 0.00%