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. 25, 2014	Apr. 26, 2013	Apr. 27, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 42.0	$ 51.0	$ 65.1
Total unrealized gains, net included in OCI	1.3	0.5	0.9
Total realized gains included in earnings	0.7	1.1	0.7
Sales	(8.0)	0	0
Settlements	0	(10.6)	(15.7)
Balance at end of period	$ 36.0	$ 42.0	$ 51.0