Derivatives and Hedging Activities - Schedule of Notional Value of Outstanding Foreign Currency Forward Contracts (Detail) (USD $) In Millions, unless otherwise specified	Jan. 25, 2013	Apr. 27, 2012
Euro
Derivative [Line Items]
Cash Flow Hedges	$ 146.9	$ 96.9
Balance Sheet Contracts	180.5	267.4
British Pound Sterling
Derivative [Line Items]
Cash Flow Hedges	26.9	29.8
Balance Sheet Contracts	48.3	86.4
Australian Dollar
Derivative [Line Items]
Balance Sheet Contracts	91.6	54.3
Israeli Shekel
Derivative [Line Items]
Balance Sheet Contracts	22.3	17.2
Canadian Dollar
Derivative [Line Items]
Balance Sheet Contracts	19.7	38.5
Swiss Franc
Derivative [Line Items]
Balance Sheet Contracts	10.3	7.3
Other
Derivative [Line Items]
Balance Sheet Contracts	$ 46.8	$ 44.0