Commitments and Contingencies - Schedule of Warranty Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 25, 2013	Jan. 27, 2012	Jan. 25, 2013	Jan. 27, 2012
Commitments and Contingencies [Line Items]
Beginning balance	$ 111.8	$ 65.0	$ 83.1	$ 40.5
Liability assumed in acquisition	0	0	0	17.5
Expense accrued during the period	23.5	14.1	74.3	41.5
Warranty costs incurred	(18.5)	(10.9)	(40.6)	(31.3)
Ending balance	$ 116.8	$ 68.2	$ 116.8	$ 68.2