Stockholders' Equity - Reconciliation of Retained Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jul. 25, 2014	Jul. 26, 2013
Retained Earnings Adjustments [Line Items]
Beginning balance	$ 1.1
Net income	88.4	81.6
Dividends	(53.4)	(51.4)
Ending balance	36.1
Retained Earnings
Retained Earnings Adjustments [Line Items]
Dividends	$ (53.4)	$ (51.4)