Purchased Intangible Assets Net (Detail) (USD $) In Millions, unless otherwise specified	Oct. 24, 2014	Apr. 25, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Assets	$ 288.5	$ 297.1
Accumulated Amortization	(196.0)	(175.6)
Net Assets	92.5	121.5
Developed Technology
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Assets	283.0	283.0
Accumulated Amortization	(191.1)	(162.6)
Net Assets	91.9	120.4
Customer Contracts/Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Assets	2.6	9.6
Accumulated Amortization	(2.2)	(9.0)
Net Assets	0.4	0.6
Trademarks And Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Assets	2.9	2.9
Accumulated Amortization	(2.7)	(2.4)
Net Assets	0.2	0.5
Covenants not to Compete
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Assets	0	1.6
Accumulated Amortization	0	(1.6)
Net Assets	$ 0	$ 0