v3.26.1
Investment in Securities - Additional Information (Detail)
¥ in Millions
12 Months Ended
Mar. 31, 2026
JPY (¥)
Investment
Mar. 31, 2025
JPY (¥)
Investment
Mar. 31, 2024
JPY (¥)
Schedule of Investments [Line Items]      
Net unrealized holding gains (losses) on trading securities ¥ 170,073 ¥ 4,422 ¥ 53,318
Proceeds from sales of available-for-sale debt securities 341,135 299,890 215,674
Available-for-sale debt securities gross realized gains 3,732 8,499 4,137
Available-for-sale debt securities gross realized losses 7,709 16,517 11,090
Investment funds fair value ¥ 39,796 ¥ 41,018  
Number of investment securities in an unrealized loss position | Investment 1,113 1,272  
Accrued interest on available-for-sale debt securities ¥ 14,697 ¥ 14,545  
Allowance for credit losses for accrued interest receivables ¥ 0 0  
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Other Assets    
Interest income on investment securities ¥ 37,814 29,140 26,331
Equity securities      
Schedule of Investments [Line Items]      
Investment funds fair value 24,845 24,960  
Trading Debt Securities      
Schedule of Investments [Line Items]      
Net unrealized holding gains (losses) on trading debt securities 0 0 ¥ (96)
Available-for-sale securities | Foreign Government Bond Securities      
Schedule of Investments [Line Items]      
Investment funds fair value 3,024 5,379  
Available-for-sale securities | Foreign Corporate Debt Securities      
Schedule of Investments [Line Items]      
Investment funds fair value ¥ 11,927 ¥ 10,679