Goodwill and Purchased Intangible Assets Net - Amortization Expense for Purchased Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 25, 2013	Jan. 27, 2012	Jan. 25, 2013	Jan. 27, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 21.4	$ 21.6	$ 64.3	$ 67.6
Developed Technology
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	13.9	14.0	41.8	41.9
Customer Contracts/Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	6.3	6.4	18.9	21.8
Trademarks And Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	1.1	1.0	3.1	3.3
Covenants Not To Compete
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 0.1	$ 0.2	$ 0.5	$ 0.6