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, unless otherwise specified	12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2011
Assets: [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on assets	¥ 12	[1]	¥ (8)	[1]	¥ 10	[1]
Trading assets [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on assets	2	[1],[2]	0	[1],[2]	(4)	[1],[2]
Private equity investments [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on assets	(10)	[1],[2]	(12)	[1],[2]	0	[1],[2]
Loans and receivables [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on assets	19	[1]	(6)	[1]	8	[1]
Collateralized agreements [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on assets	0	[1],[3]	10	[1],[3]	6	[1],[3]
Other [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on assets	1	[1],[2]	0	[1],[2]
Liabilities: [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on liabilities	(56)	[1]	(26)	[1]	(44)	[1]
Short-term borrowings [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on liabilities	(4)	[1],[4]	(14)	[1],[4]	(7)	[1],[4]
Collateralized financing [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on liabilities	(1)	[1],[3]	(1)	[1],[3]	0	[1],[3]
Long-term borrowings [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on liabilities	(51)	[1],[4],[5]	(11)	[1],[4],[5]	(37)	[1],[4],[5]
Other liabilities [Member]
Fair value, balance sheet grouping, financial statement captions [Line Items]
Gains (Losses) on liabilities	¥ 0	[1],[6]	¥ 0	[1],[6]

[1] Includes gains and losses reported primarily within Net gain on trading and Gain on private equity investments in the consolidated statements of income.

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

[3] Includes resale and repurchase agreements.

[4] Includes structured notes and other financial liabilities.

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

[6] Includes loan commitments.