v3.26.1
Non-trading investments - Additional Information (Detail) - Non-BD entities other than investment companies [Member] - JPY (¥)
¥ in Millions
12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Equity Securities without Readily Determinable Fair Value [Line Items]    
Non-trading equity investments elected for the fair value measurement alternative ¥ 102,546 ¥ 95,529
Unrealized gains (losses) on equity securities owned by non-BD entities that are not investment companies ¥ 12,452 ¥ 2,630