Financing Arrangements - Amount of Interest Expense Recognized Related to Convertible Notes (Detail) (Convertible Notes Payable, USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Jan. 25, 2013	Jan. 24, 2014	Jan. 25, 2013
Convertible Notes Payable
Debt Instrument [Line Items]
Contractual coupon interest expense	$ 5.5	$ 2.5	$ 16.5
Amortization of debt discount	13.9	7.1	41.0
Amortization of debt issuance costs	1.2	0.6	3.6
Less capitalized interest	0	0	(1.1)
Total interest expense related to Convertible Notes	$ 20.6	$ 10.2	$ 60.0