Employee Stock and Savings Plans Fair Value Calculation Assumptions (Details)	12 Months Ended
Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions
Risk-free interest rate, minimum	0.05%	0.09%	0.05%
Risk-free interest rate, maximum	0.09%	0.14%	0.15%
Dividend yield	0.80%	0.50%	0.00%
Expected term	0 years 6 months 0 days	0 years 6 months 0 days	0 years 6 months 0 days
Volatility, minimum	22.00%	22.00%	33.00%
Volatility, maximum	23.00%	33.00%	43.00%
Weighted average volatility rate	22.00%	29.00%	39.00%
Employee Stock Purchase Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions
Dividend yield	0.80%	0.00%	0.00%
Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions
Dividend yield	0.90%	1.00%	0.00%
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions
Risk-free interest rate, minimum			0.90%
Risk-free interest rate, maximum			1.30%
Dividend yield			0.00%
Volatility, minimum			43.00%
Volatility, maximum			53.00%
Weighted average volatility rate			43.00%
Stock Options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions
Expected term			5 years 9 months 18 days
Stock Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions
Expected term			6 years 3 months 18 days

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(iii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.D.2)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section D

-Subsection 2

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- Definition

The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

+ Details

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- Definition

The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

+ Details

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- Definition

The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

No definition available.

+ Details

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- Definition

The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

No definition available.

+ Details

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- Definition

Weighted average expected volatility rate of share-based compensation awards.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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