Financial Instruments and Fair Value Measurements - Reconciliation of Beginning and Ending Balance of Level Three Auction Rate Securities Measured at Fair Value On Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 26, 2013	Apr. 27, 2012	Apr. 29, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 51.0	$ 65.1	$ 69.0
Total unrealized gains (losses), net included in other comprehensive income	0.5	0.9	(1.4)
Total realized gains included in earnings	1.1	0.7	0
Settlements	(10.6)	(15.7)	(2.5)
Balance at end of period	$ 42.0	$ 51.0	$ 65.1