Fair value measurements - Gains (losses) due to changes in fair value for financial instruments measured at fair value using fair value option (Detail) - JPY (¥) ¥ in Billions		3 Months Ended		6 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Short-term borrowings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[2]	¥ 66	¥ 33	¥ 126	¥ 21
Payables and deposits [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	4	0	9	3
Collateralized financing [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[3]	0	8	3	6
Long-term borrowings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[2],[4]	173	30	442	(25)
Other liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[5]	11	(6)	16	(10)
Total [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	254	65	596	(5)
Trading assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[6]	(1)		(1)	0
Private equity and debt investments [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[6]	1	1	2	1
Loans and receivables [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	7	4	16	8
Collateralized agreements [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[3]	(2)	0	(2)	0
Other assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[6]	(10)	5	(35)	16
Total [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	¥ (5)	¥ 10	¥ (20)	¥ 25

[1] Includes gains and losses reported primarily within Revenue—Net gain on trading and Revenue—Other in the consolidated statements of income.

[2] Includes structured notes and other financial liabilities.

[3] Includes reverse repurchase and repurchase agreements.

[4] Includes secured financing transactions arising from transfers of financial assets which did not meet the criteria for sales accounting.

[5] Includes unfunded written loan commitments.

[6] Includes equity investments that would have been accounted for under the equity method had Nomura not chosen to elect the fair value option.