Acquisitions - Summary of Fair Value of Assets Acquired and Liabilities Assumed by Major Class (Detail) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 1,561.1	$ 1,535.0
Increase (decrease) in deferred tax liabilities	38.8	(235.9)	$ 18.8
Other
Business Acquisition [Line Items]
Goodwill	62.8	63.7
Deferred revenue (current and non-current)	(2.1)	(0.7)
Deferred tax liability	(7.1)	(1.6)
Net tangible (liabilities) assets	0.6	0.5
Total	87.0	106.8
Other | Developed technologies
Business Acquisition [Line Items]
Intangible assets	18.8	27.3
Other | Customer Relationships And Other Noncurrent Intangible Assets
Business Acquisition [Line Items]
Intangible assets	10.2	12.9
Other | Trade name
Business Acquisition [Line Items]
Intangible assets	3.8	4.7
netfabb
Business Acquisition [Line Items]
Goodwill		36.1
Deferred revenue (current and non-current)		(1.0)
Deferred tax liability		(3.9)
Net tangible (liabilities) assets		(2.9)
Total		42.5
netfabb | Developed technologies
Business Acquisition [Line Items]
Intangible assets		6.6
netfabb | Customer Relationships And Other Noncurrent Intangible Assets
Business Acquisition [Line Items]
Intangible assets		6.2
netfabb | Trade name
Business Acquisition [Line Items]
Intangible assets		$ 1.4
Measurement Period Adjustment 1
Business Acquisition [Line Items]
Goodwill, period increase (decrease)	3.3
Increase (decrease) in tangible liabilities	3.3
Measurement Period Adjustment 2
Business Acquisition [Line Items]
Goodwill, period increase (decrease)	(0.8)
Increase (decrease) in deferred tax liabilities	$ (0.8)