Acquisitions Summary of Fair Value of Assets Acquired and Liabilities Assumed by Major Class (Details) - USD ($) $ in Millions	Apr. 30, 2016	Jan. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 1,580.5	$ 1,535.0
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Goodwill	45.4
Deferred revenue (current and non-current)	(0.3)
Deferred tax liability	(2.8)
Net tangible assets	0.4
Total	61.3
Series of Individually Immaterial Business Acquisitions | Developed technologies
Business Acquisition [Line Items]
Finite-lived intangibles	11.5
Series of Individually Immaterial Business Acquisitions | Customer relationships and other non-current intangible assets
Business Acquisition [Line Items]
Finite-lived intangibles	4.6
Series of Individually Immaterial Business Acquisitions | Trade name
Business Acquisition [Line Items]
Finite-lived intangibles	$ 2.5