Commitments and Contingencies - Schedule of Warranty Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 26, 2012	Oct. 28, 2011	Oct. 26, 2012	Oct. 28, 2011
Commitments and Contingencies [Line Items]
Beginning balance	$ 96.5	$ 59.5	$ 83.1	$ 40.5
Liability assumed in acquisition	0	0	0	17.5
Expense accrued during the period	27.1	15.7	50.8	27.4
Warranty costs incurred	(11.8)	(10.2)	(22.1)	(20.4)
Ending balance	$ 111.8	$ 65.0	$ 111.8	$ 65.0