Financial Instruments And Fair Value (Reconciliation Of Beginning And Ending Balance Of Level 3 Auction Rate Securities Measured At Fair Value On Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 27, 2012	Jan. 28, 2011	Jan. 27, 2012	Jan. 28, 2011
Financial Instruments And Fair Value [Abstract]
Balance at beginning of period	$ 56.0	$ 66.2	$ 65.1	$ 69.0
Total unrealized gains (losses), net included in other comprehensive income	(0.7)	(0.5)	0.6	(1.9)
Total realized gains included in earnings	0.7	0	0.7	0
Settlements	(5.0)	(0.6)	(15.4)	(2.0)
Balance at end of period	$ 51.0	$ 65.1	$ 51.0	$ 65.1