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	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share [Line Items]
Basic-Net income attributable to NHI shareholders	¥ 107,234	¥ 11,583	¥ 28,661
Basic-Weighted average number of shares outstanding	3,692,795,953	3,643,481,439	3,627,798,587
Basic-Net income attributable to NHI shareholders per share	¥ 29.04	¥ 3.18	¥ 7.90
Diluted-Net income attributable to NHI shareholders	¥ 107,181	¥ 11,561	¥ 28,642
Diluted-Weighted average number of shares outstanding	3,777,360,671	3,680,124,235	3,642,689,381
Diluted-Net income attributable to NHI shareholders per share	¥ 28.37	¥ 3.14	¥ 7.86

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

12 Months Ended

Mar. 31, 2013

Mar. 31, 2012

Mar. 31, 2011

Earnings Per Share [Line Items]

Basic-Net income attributable to NHI shareholders

¥ 107,234

¥ 11,583

¥ 28,661

Basic-Weighted average number of shares outstanding

3,692,795,953

3,643,481,439

3,627,798,587

Basic-Net income attributable to NHI shareholders per share

¥ 29.04

¥ 3.18

¥ 7.90

Diluted-Net income attributable to NHI shareholders

¥ 107,181

¥ 11,561

¥ 28,642

Diluted-Weighted average number of shares outstanding

3,777,360,671

3,680,124,235

3,642,689,381

Diluted-Net income attributable to NHI shareholders per share

¥ 28.37

¥ 3.14

¥ 7.86

- Definition

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

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

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+ Details

- Definition

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.

+ References+ Details

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6519514

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-Publisher SEC

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-Number 210

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

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-Name Emerging Issues Task Force (EITF)

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph A7

-Appendix A

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-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph a

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Reference 16: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

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.

+ References+ Details

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 40

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-Publisher FASB

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-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 07-4

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Weighted-Average Number of Common Shares Outstanding

-URI http://asc.fasb.org/extlink&oid=6528421

+ Details