Acquisitions Summary of Fair Value of Assets Acquired and Liabilities Assumed by Major Class (Details) - USD ($) $ in Millions	Jul. 31, 2016	Jan. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 1,597.4	$ 1,535.0
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Goodwill	62.8
Deferred revenue (current and non-current)	(2.1)
Deferred tax liability	(7.1)
Net tangible assets	0.6
Total	87.0
Series of Individually Immaterial Business Acquisitions | Developed technologies
Business Acquisition [Line Items]
Finite-lived intangibles	18.8
Series of Individually Immaterial Business Acquisitions | Customer relationships and other non-current intangible assets
Business Acquisition [Line Items]
Finite-lived intangibles	10.2
Series of Individually Immaterial Business Acquisitions | Trade name
Business Acquisition [Line Items]
Finite-lived intangibles	$ 3.8