v3.26.1
Borrowings - Additional information (Detail) - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Schedule of Borrowings [Line Items]    
Unutilized borrowing facilities
Subordinated borrowings ¥ 874,309 ¥ 414,500
Fixed-rate obligations [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, Maturities start period 2026 2025
Long-term borrowings, Maturities end period 2067 2067
Fixed-rate obligations [Member] | Minimum [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, interest rate 0.00% 0.00%
Fixed-rate obligations [Member] | Maximum [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, interest rate 37.10% 44.00%
Floating-rate obligations [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, Maturities start period 2026 2025
Long-term borrowings, Maturities end period 2070 2069
Floating-rate obligations [Member] | Minimum [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, interest rate 0.00% 0.00%
Floating-rate obligations [Member] | Maximum [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, interest rate 12.89% 17.00%
Index / Equity-linked obligations [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, Maturities start period 2026 2025
Long-term borrowings, Maturities end period 2056 2055
Index / Equity-linked obligations [Member] | Minimum [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, interest rate 0.00% 0.00%
Index / Equity-linked obligations [Member] | Maximum [Member]    
Schedule of Borrowings [Line Items]    
Long-term borrowings, interest rate 45.00% 36.80%