v3.25.2
Severance Indemnities and Pension Plans (Weighted-average Target Asset Allocation of Plan Assets for Pension Benefits and Other Benefits) (Detail)
Mar. 31, 2025
Domestic, Japan | Pension benefits and SIPs  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 100.00%
Domestic, Japan | Pension benefits and SIPs | Japanese equity securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 35.60%
Domestic, Japan | Pension benefits and SIPs | Japanese debt securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 23.00%
Domestic, Japan | Pension benefits and SIPs | Non-Japanese equity securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 13.50%
Domestic, Japan | Pension benefits and SIPs | Non-Japanese debt securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 21.70%
Domestic, Japan | Pension benefits and SIPs | Real estate  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 1.20%
Domestic, Japan | Pension benefits and SIPs | Short-term assets and other  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 5.00%
Foreign offices and subsidiaries | Pension benefits  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 100.00%
Foreign offices and subsidiaries | Pension benefits | Japanese equity securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 0.00%
Foreign offices and subsidiaries | Pension benefits | Japanese debt securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 0.00%
Foreign offices and subsidiaries | Pension benefits | Non-Japanese equity securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 29.80%
Foreign offices and subsidiaries | Pension benefits | Non-Japanese debt securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 61.30%
Foreign offices and subsidiaries | Pension benefits | Real estate  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 6.90%
Foreign offices and subsidiaries | Pension benefits | Short-term assets and other  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 2.00%
Foreign offices and subsidiaries | Other benefits  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 100.00%
Foreign offices and subsidiaries | Other benefits | Japanese equity securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 0.00%
Foreign offices and subsidiaries | Other benefits | Japanese debt securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 0.00%
Foreign offices and subsidiaries | Other benefits | Non-Japanese equity securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 30.00%
Foreign offices and subsidiaries | Other benefits | Non-Japanese debt securities  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 64.00%
Foreign offices and subsidiaries | Other benefits | Real estate  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 6.00%
Foreign offices and subsidiaries | Other benefits | Short-term assets and other  
Defined Benefit Plan Disclosure [Line Items]  
Target allocation of plan assets 0.00%