Earnings per share - Earnings per share (Basic and Diluted) (Detail) - JPY (¥) ¥ / shares in Units, ¥ in Millions	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Basic-
Basic-Net income attributable to NHI shareholders	¥ 239,617	¥ 131,550	¥ 224,785
Basic-Weighted average number of shares outstanding	3,560,775,652	3,600,701,499	3,645,514,878
Basic-Net income attributable to NHI shareholders per share	¥ 67.29	¥ 36.53	¥ 61.66
Diluted-
Diluted-Net income attributable to NHI shareholders	¥ 239,475	¥ 131,426	¥ 224,726
Diluted-Weighted average number of shares outstanding	3,647,729,909	3,700,388,050	3,743,690,088
Diluted-Net income attributable to NHI shareholders per share	¥ 65.65	¥ 35.52	¥ 60.03

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent, and includes adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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