v3.26.1
Non-trading investments - Summary of AFS debt securities categorized by remaining contractual maturity (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Available-for-Sale Securities, Debt Maturities [Abstract]    
Amortized cost, Total [1] ¥ 276,252 ¥ 108,704
Fair value, Total 271,344 107,030
Japanese government securities [Member]    
Available-for-Sale Securities, Debt Maturities [Abstract]    
Amortized cost,less than 1 year [1] 19,997  
Amortized cost,1 year to 5 years [1] 79,980 25,001
Amortized cost, Total [1] 99,977 25,001
Fair value, less than 1 year 19,961  
Fair value, 1 year to 5 years 79,523 24,814
Fair value, Total 99,484 24,814
Japanese agency and municipal securities [Member]    
Available-for-Sale Securities, Debt Maturities [Abstract]    
Amortized cost,less than 1 year [1] 1,395  
Amortized cost,1 year to 5 years [1] 159,244 81,913
Amortized cost, Total [1] 160,639 81,913
Fair value, less than 1 year 1,387  
Fair value, 1 year to 5 years 155,123 80,437
Fair value, Total 156,510 80,437
Bank and corporate debt securities [Member]    
Available-for-Sale Securities, Debt Maturities [Abstract]    
Amortized cost,1 year to 5 years [1] 15,636 1,790
Amortized cost, Total [1] 15,636 1,790
Fair value, 1 year to 5 years 15,350 1,779
Fair value, Total ¥ 15,350 ¥ 1,779
[1] No allowances for credit losses have been recognized as of March 31, 2025 and 2026.