Employee and Director Stock Plans - Intrinsic Value of Options Exercised and Weighted Average Grant Date Fair Value of Stock Options Granted (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Pre-tax intrinsic value of options exercised	$ 9.7	$ 22.8	$ 32.0
Weighted average grant date fair value per share of stock options assumed from acquisition (in dollars per share)	$ 110.40	$ 0	$ 0

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://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=109197908&loc=d3e5070-113901

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration