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
Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Pre-tax intrinsic value of options exercised	$ 22.8	$ 32.0	$ 32.6

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.

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=96867065&loc=d3e5070-113901

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Balance Type:	debit
Period Type:	duration