Earnings per share - Summary of Amounts and Numbers Used in Calculation of Net Income Attributable to NHI Shareholders Per Share (Basic and Diluted) (Detail) (JPY ¥) In Millions, except Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings per share
Basic-Net income attributable to NHI shareholders	¥ 52,872us-gaap_NetIncomeLoss	¥ 38,112us-gaap_NetIncomeLoss	¥ 72,732us-gaap_NetIncomeLoss	¥ 104,006us-gaap_NetIncomeLoss
Basic-Weighted average number of shares outstanding	3,638,479,123	3,704,475,301	3,660,114,608	3,705,694,494
Basic-Net income attributable to NHI shareholders per share	¥ 14.53us-gaap_EarningsPerShareBasic	¥ 10.29us-gaap_EarningsPerShareBasic	¥ 19.87us-gaap_EarningsPerShareBasic	¥ 28.07us-gaap_EarningsPerShareBasic
Diluted-Net income attributable to NHI shareholders	¥ 52,861	¥ 38,107	¥ 72,714	¥ 103,983
Diluted-Weighted average number of shares outstanding	3,736,423,754	3,813,266,130	3,759,340,816	3,822,691,418
Diluted-Net income attributable to NHI shareholders per share	¥ 14.15us-gaap_EarningsPerShareDiluted	¥ 9.99us-gaap_EarningsPerShareDiluted	¥ 19.34us-gaap_EarningsPerShareDiluted	¥ 27.20us-gaap_EarningsPerShareDiluted

Earnings per share - Summary of Amounts and Numbers Used in Calculation of Net Income Attributable to NHI Shareholders Per Share (Basic and Diluted) (Detail) (JPY ¥)
In Millions, except Share data, unless otherwise specified

3 Months Ended

6 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Earnings per share

Basic-Net income attributable to NHI shareholders

¥ 52,872us-gaap_NetIncomeLoss

¥ 38,112us-gaap_NetIncomeLoss

¥ 72,732us-gaap_NetIncomeLoss

¥ 104,006us-gaap_NetIncomeLoss

Basic-Weighted average number of shares outstanding

3,638,479,123us-gaap_WeightedAverageNumberOfSharesOutstandingBasic

3,704,475,301us-gaap_WeightedAverageNumberOfSharesOutstandingBasic

3,660,114,608us-gaap_WeightedAverageNumberOfSharesOutstandingBasic

3,705,694,494us-gaap_WeightedAverageNumberOfSharesOutstandingBasic

Basic-Net income attributable to NHI shareholders per share

¥ 14.53us-gaap_EarningsPerShareBasic

¥ 10.29us-gaap_EarningsPerShareBasic

¥ 19.87us-gaap_EarningsPerShareBasic

¥ 28.07us-gaap_EarningsPerShareBasic

Diluted-Net income attributable to NHI shareholders

¥ 52,861us-gaap_NetIncomeLossAttributableToParentDiluted

¥ 38,107us-gaap_NetIncomeLossAttributableToParentDiluted

¥ 72,714us-gaap_NetIncomeLossAttributableToParentDiluted

¥ 103,983us-gaap_NetIncomeLossAttributableToParentDiluted

Diluted-Weighted average number of shares outstanding

3,736,423,754us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

3,813,266,130us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

3,759,340,816us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

3,822,691,418us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

Diluted-Net income attributable to NHI shareholders per share

¥ 14.15us-gaap_EarningsPerShareDiluted

¥ 9.99us-gaap_EarningsPerShareDiluted

¥ 19.34us-gaap_EarningsPerShareDiluted

¥ 27.20us-gaap_EarningsPerShareDiluted

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