Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Jan. 25, 2013	Jan. 25, 2013
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 170.0	$ 170.0
Unrecognized tax benefits included in other long-term liabilities	116.8	116.8
Unrecognized tax benefits that would affect provision for income taxes	100.8	100.8
Gross increase in unrecognized tax benefits for tax positions related to the current year		14.8
Gross increase in unrecognized tax benefits for tax positions related to the prior year		1.0
Gross decrease in unrecognized tax benefits for tax positions related to the prior year		6.8
Current year research credit
Income Tax Contingency [Line Items]
Research credit benefit	8.2	8.2
Prior year research credit
Income Tax Contingency [Line Items]
Research credit benefit	$ 3.2	$ 3.2