Acquisitions - Summary of Fair Value of Assets Acquired and Liabilities Assumed by Major Class (Detail) - USD ($) $ in Millions	Jan. 31, 2018	Jan. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 1,620.2	$ 1,561.1
Other
Business Acquisition [Line Items]
Goodwill		62.8
Deferred revenue (current and non-current)		(2.1)
Deferred tax liability		(7.1)
Net tangible (liabilities) assets		0.6
Total		87.0
Other | Developed technologies
Business Acquisition [Line Items]
Intangible assets		18.8
Other | Customer relationships
Business Acquisition [Line Items]
Intangible assets		10.2
Other | Trade name
Business Acquisition [Line Items]
Intangible assets		$ 3.8