Revenue from services provided to customers - Additional information (Detail) - JPY (¥) ¥ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from performance obligations satisfied in previous periods	¥ 1,817	¥ 458	¥ 5,930	¥ 538
Remaining performance obligations, Transaction price	¥ 1,657		¥ 1,657		¥ 1,187
Estimated contract period			1 year		1 year

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details