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		12 Months Ended
		Mar. 31, 2022		Mar. 31, 2021		Mar. 31, 2020
Short-term borrowings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[2]	¥ 60		¥ (83)		¥ 64
Payables and deposits [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	4		3		0
Collateralized financing [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[3]	3		9		(2)
Long-term borrowings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[2],[4]	275		(194)		58
Other liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[5]	4		3		2
Total [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	346		(262)		122
Trading assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[6]	1		2	[1]	1
Private equity and debt investments [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	6		0		(1)
Loans and receivables [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	39		7		2
Collateralized agreements [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)		(1)	[3]	5	[1]	4	[3]
Other assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[6]	(3)		51	[1]	(16)
Total [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	¥ 42		¥ 65		¥ (10)

[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.