Revenue from services provided to customers - Schedule of Disaggregation of Asset Management Fees And Custody Fee (Detail) - JPY (¥) ¥ in Millions	3 Months Ended	6 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation Of Asset Management Fees And Custody Fee [Abstract]
Asset management fees	¥ 47,630	¥ 43,197	¥ 92,865	¥ 86,917
Administration fees	22,002	19,623	42,005	38,578
Custodial fees	7,034	6,218	13,603	11,793
Total	¥ 76,666	¥ 69,038	¥ 148,473	¥ 137,288

Revenue recognized in the period for (1) performance(incentive) fees based on the investment results achieved for management of certain institutional accounts and hedge funds, (2) schedule-based fees earned for management of mutual funds and closed-end funds, based either on average daily net assets or on a combination of the average daily net assets and gross income, and (3) other investment management and advisory fees, (4) fees charged for services related to holding, advising, and managing customer investment assets.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration