Computation of the Numerators and Denominators Used in the Basic and Diluted Net Income Per Share Amounts (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Numerator:
Net income	$ 72.8	$ 53.6	$ 213.3	$ 150.4
Denominator:
Denominator for basic net income per share-weighted average shares	227.1	226.5	228.2	227.9
Effect of dilutive securities	3.6	5.9	5.5	5.5
Denominator for dilutive net income per share	230.7	232.4	233.7	233.4
Basic net income per share	$ 0.32	$ 0.24	$ 0.93	$ 0.66
Diluted net income per share	$ 0.32	$ 0.23	$ 0.91	$ 0.64

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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-Topic 260

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-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6920599&loc=d3e1252-109256

+ 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

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph A7

-Appendix A

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-Glossary Other Comprehensive Income

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

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-Publisher AICPA

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

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

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-Publisher FASB

-Name Accounting Standards Codification

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

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+ Details

- Definition

The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

+ References+ 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

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

-Publisher FASB

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-Glossary Weighted-Average Number of Common Shares Outstanding

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

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