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		3 Months Ended		6 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Derivative [Line Items]
Gains (losses) on derivatives used for trading and non-trading purposes	[1]	¥ 243	¥ (151)	¥ 453	¥ (108)
Equity contracts [Member]
Derivative [Line Items]
Gains (losses) on derivatives used for trading and non-trading purposes	[1]	14	(117)	(20)	(185)
Interest rate contracts [Member]
Derivative [Line Items]
Gains (losses) on derivatives used for trading and non-trading purposes	[1]	190	7	302	16
Credit contracts [Member]
Derivative [Line Items]
Gains (losses) on derivatives used for trading and non-trading purposes	[1]	4	(8)	(101)	2
Foreign exchange contracts [Member]
Derivative [Line Items]
Gains (losses) on derivatives used for trading and non-trading purposes	[1]	55	(43)	270	26
Commodity contracts [Member]
Derivative [Line Items]
Gains (losses) on derivatives used for trading and non-trading purposes	[1]	¥ (20)	¥ 10	¥ 2	¥ 33

[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 six and three months ended September 30, 2021 and 2022, these amounts have not been separately presented as net gains (losses) for these non-trading derivatives were not significant.