Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) by Component Net of Tax (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 24, 2015	Apr. 25, 2014	Apr. 26, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 9.1	$ 8.7
OCI before reclassifications, net of tax	(18.3)	(0.7)
Amounts reclassified from AOCI, net of tax	(14.5)	1.1
Other comprehensive income (loss)	(32.8)	0.4	3.8
Ending balance	(23.7)	9.1	8.7
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	5.5	2.0
OCI before reclassifications, net of tax	(28.3)	3.5
Amounts reclassified from AOCI, net of tax	0	0
Other comprehensive income (loss)	(28.3)	3.5
Ending balance	(22.8)	5.5
Defined Benefit Obligation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4.8)	(5.7)
OCI before reclassifications, net of tax	(7.8)	0.5
Amounts reclassified from AOCI, net of tax	0.2	0.4
Other comprehensive income (loss)	(7.6)	0.9
Ending balance	(12.4)	(4.8)
Unrealized Gains on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	8.9	11.4
OCI before reclassifications, net of tax	2.3	(1.2)
Amounts reclassified from AOCI, net of tax	(0.3)	(1.3)
Other comprehensive income (loss)	2.0	(2.5)
Ending balance	10.9	8.9
Unrealized Gains (Losses) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(0.5)	1.0
OCI before reclassifications, net of tax	15.5	(3.5)
Amounts reclassified from AOCI, net of tax	(14.4)	2.0
Other comprehensive income (loss)	1.1	(1.5)
Ending balance	$ 0.6	$ (0.5)