Acquisitions Summary of Fair Value of Assets Acquired and Liabilities Assumed by Major Class (Details) - USD ($) $ in Millions	Oct. 31, 2015	Jan. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 1,515.0	$ 1,456.2
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Goodwill	63.4
Deferred revenue (current and non-current)	0.7
Deferred tax liability	(2.4)
Net tangible assets	0.5
Total	105.0
Series of Individually Immaterial Business Acquisitions | Developed technologies
Business Acquisition [Line Items]
Finite-lived intangibles	26.8
Series of Individually Immaterial Business Acquisitions | Customer relationships and other non-current intangible assets
Business Acquisition [Line Items]
Finite-lived intangibles	12.8
Series of Individually Immaterial Business Acquisitions | Trade name
Business Acquisition [Line Items]
Finite-lived intangibles	$ 4.6