Stockholders Equity - Accumulated Other Comprehensive Income (Loss) by Component Net of Tax (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jul. 25, 2014	Jul. 26, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 9.1
Other comprehensive income (loss) (OCI) before reclassifications	(2.0)
Amounts reclassified from AOCI, net of tax	2.0
Other comprehensive income (loss)	0	(10.0)
Ending balance	9.1
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	5.5
Other comprehensive income (loss) (OCI) before reclassifications	(0.8)
Amounts reclassified from AOCI, net of tax	0
Other comprehensive income (loss)	(0.8)
Ending balance	4.7
Defined Benefit Obligation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4.8)
Other comprehensive income (loss) (OCI) before reclassifications	1.0
Amounts reclassified from AOCI, net of tax	0.1
Other comprehensive income (loss)	1.1
Ending balance	(3.7)
Unrealized Gains on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	8.9
Other comprehensive income (loss) (OCI) before reclassifications	(1.6)
Amounts reclassified from AOCI, net of tax	0.2
Other comprehensive income (loss)	(1.4)
Ending balance	7.5
Unrealized Gains (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(0.5)
Other comprehensive income (loss) (OCI) before reclassifications	(0.6)
Amounts reclassified from AOCI, net of tax	1.7
Other comprehensive income (loss)	1.1
Ending balance	$ 0.6