v3.26.3
Investment in Securities - Additional Information (Detail)
¥ in Millions
6 Months Ended
Sep. 30, 2026
JPY (¥)
Investment
Sep. 30, 2025
JPY (¥)
Mar. 31, 2026
JPY (¥)
Investment
Schedule of Investments [Line Items]      
Net unrealized holding gains (losses) on trading securities ¥ 100,176 ¥ 64,149  
Investment funds fair value ¥ 51,788   ¥ 39,796
Number of investment securities in an unrealized loss position | Investment 1,144   903
Debt securities available-for-sale accrued interest, after allowance for credit loss ¥ 16,054   ¥ 14,393
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Other Assets    
Net unrealized holding gains (losses) on trading debt securities held   ¥ 5  
Allowance for credit losses for accrued interest receivables ¥ 0   0
Debt securities, trading, gain (loss) 0    
Equity securities      
Schedule of Investments [Line Items]      
Investment funds fair value 25,231   24,845
Available-for-sale securities | Foreign Government Bond Securities      
Schedule of Investments [Line Items]      
Investment funds fair value 17,551   3,024
Available-for-sale securities | Foreign Corporate Debt Securities      
Schedule of Investments [Line Items]      
Investment funds fair value ¥ 9,006   ¥ 11,927