v3.26.1
Derivative instruments and hedging activities - Schedule of derivatives used for trading and non-trading purposes (Detail) - Derivatives used for trading and non-trading purposes [Member] - JPY (¥)
¥ in Billions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Derivative [Line Items]      
Gains (losses) on derivatives used for trading and non-trading purposes [1] ¥ (249) ¥ (13) ¥ 455
Equity contracts [Member]      
Derivative [Line Items]      
Gains (losses) on derivatives used for trading and non-trading purposes [1] (272) (2) (194)
Interest rate contracts [Member]      
Derivative [Line Items]      
Gains (losses) on derivatives used for trading and non-trading purposes [1] 106 (189) 468
Credit contracts [Member]      
Derivative [Line Items]      
Gains (losses) on derivatives used for trading and non-trading purposes [1] 46 27 12
Foreign exchange contracts [Member]      
Derivative [Line Items]      
Gains (losses) on derivatives used for trading and non-trading purposes [1] (175) 140 142
Other contracts [Member]      
Derivative [Line Items]      
Gains (losses) on derivatives used for trading and non-trading purposes [1] ¥ 46 ¥ 11 ¥ 27
[1] Includes net gains (losses) on derivatives used for non-trading purposes which are not designated as fair value or net investment hedges. For the year ended March 31, 2024, 2025 and 2026, net gains (losses) for these non-trading derivatives were not significant.