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Employee and Director Stock Plans - Intrinsic Value of Options Exercised and Weighted Average Grant Date Fair Value of Stock Options Granted (Detail) - USD ($) $ in Millions | 12 Months Ended
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Jan. 31, 2017 | Jan. 31, 2016 | Jan. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |  |  |  |
Pre-tax intrinsic value of options exercised | [1] | $ 32.0 | $ 32.6 | $ 67.6
[1] | e intrinsic value of options exercised is calculated as the difference between the exercise price of the option and the market value of the stock on the date of exercise.

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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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