Restructuring and Other Charges - Activities Related to Restructuring Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 24, 2014	Oct. 25, 2013	Oct. 24, 2014	Oct. 25, 2013
Restructuring Cost and Reserve [Line Items]
Net charges	$ 0	$ 1.1	$ 0	$ 49.5
May 2013 Restructuring
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period				0
Net charges				49.5
Cash payments				(45.4)
Balance at end of period		4.1		4.1
March 2014 Restructuring
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period			26.5
Net charges			0
Cash payments			(25.4)
Balance at end of period	$ 1.1		$ 1.1