Derivative instruments and hedging activities - Schedule of gains (losses) from derivatives and non-derivatives designated as net investment hedges (Detail) - Net investment hedging instruments [Member] - JPY (¥) ¥ in Billions	3 Months Ended		6 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivatives designated as net investment hedges	¥ 9	¥ 4	¥ 18	¥ 2
Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivatives designated as net investment hedges	¥ 9	¥ 4	¥ 18	¥ 2