Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Apr. 28, 2012	Apr. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 321.9	$ 188.2
Derivative instruments, assets	0.2	5.5
Total assets	322.1	193.7
Derivative instruments, liabilities	0.2	5.6
Quoted Prices In Active Markets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	321.9	188.2
Total assets	321.9	188.2
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	0.2	5.5
Total assets	0.2	5.5
Derivative instruments, liabilities	$ 0.2	$ 5.6