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Stock-based Compensation Expense (Intrinsic Value of Options Exercised) (Details) - USD ($) $ in Millions | 6 Months Ended
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Jul. 31, 2019 | Jul. 31, 2018
Share-based Payment Arrangement [Abstract] |  |
Pre-tax intrinsic value of options exercised | $ 26.9 | $ 6.5

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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