Other comprehensive income (loss) - Changes in accumulated other comprehensive income (loss) (Parenthetical) (Detail) (JPY ¥) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Affected line items in consolidated statements of income [Line Items]
Income tax expense	¥ (20,894)us-gaap_IncomeTaxExpenseBenefit	¥ (34,549)us-gaap_IncomeTaxExpenseBenefit	¥ (51,291)us-gaap_IncomeTaxExpenseBenefit	¥ (81,505)us-gaap_IncomeTaxExpenseBenefit
Net income attributable to noncontrolling interests	(239)	(272)	(1,656)	(641)
Net income attributable to NHI shareholders	52,872us-gaap_NetIncomeLoss	38,112us-gaap_NetIncomeLoss	72,732us-gaap_NetIncomeLoss	104,006us-gaap_NetIncomeLoss
Reclassifications out of accumulated other comprehensive income (loss) [Member] \| Net unrealized gain on non-trading securities [Member]
Affected line items in consolidated statements of income [Line Items]
Gain (loss) on investments in equity securities	341	153	435	1,708
Income tax expense	(116)	(65)	(149)	(502)
Net income	225	88	286	1,206
Net income attributable to noncontrolling interests	(57)	(22)	(73)	(311)
Net income attributable to NHI shareholders	¥ 168	¥ 66	¥ 213	¥ 895

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of Net Income (Loss) attributable to noncontrolling interest.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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