v3.26.1
Fair value measurements - Geographic allocations of trading assets related to government, agency and municipal securities (Parenthetical) (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Fair value, concentration of credit risk [Line items]    
Non-trading debt securities ¥ 761,267 ¥ 485,290
Government, agency and municipal securities [Member]    
Fair value, concentration of credit risk [Line items]    
Non-trading debt securities ¥ 653,000 ¥ 313,000