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Business Combinations - Preliminary Fair Values of Assets Acquired and Liabilities Assumed (Detail) (USD $) In Millions, unless otherwise specified	Apr. 24, 2015	Apr. 25, 2014	Apr. 26, 2013
Business Acquisition [Line Items]
Goodwill	$ 1,027.4us-gaap_Goodwill	$ 988.1us-gaap_Goodwill	$ 988.1us-gaap_Goodwill
Fiscal 2015 Acquisitions
Business Acquisition [Line Items]
Prepaid expenses and other current assets	2.7
Finite-lived intangible assets	31.8
Goodwill	39.3
Deferred income taxes	10.8
Other non-current assets	1.1
Total assets acquired	85.7
Deferred revenue	(1.1)
Total purchase price	$ 84.6