Financing Arrangements - Amount of Interest Expense Recognized Related to Convertible Notes (Detail) (Convertible Notes Payable, USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 25, 2014	Apr. 26, 2013	Apr. 27, 2012
Convertible Notes Payable
Debt Instrument [Line Items]
Contractual coupon interest expense	$ 2.5	$ 22.0	$ 22.0
Amortization of debt discount	7.1	55.5	52.0
Amortization of debt issuance costs	0.6	4.8	4.5
Less capitalized interest	0	(1.1)	(5.0)
Total interest expense related to Convertible Notes	$ 10.2	$ 81.2	$ 73.5