Acquisitions Summary of Fair Value of Assets Acquired and Liabilities Assumed by Major Class (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2015	Jan. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 1,476.1	$ 1,456.2
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Goodwill	21.0
Deferred tax liability	(0.8)
Net tangible assets	0.5
Total	34.8
Series of Individually Immaterial Business Acquisitions | Developed technologies
Business Acquisition [Line Items]
Finite-lived intangibles	11.6
Series of Individually Immaterial Business Acquisitions | Customer relationships and other non-current intangible assets
Business Acquisition [Line Items]
Finite-lived intangibles	1.5
Series of Individually Immaterial Business Acquisitions | Trade name
Business Acquisition [Line Items]
Finite-lived intangibles	$ 1.0