Stockholders' Equity (Stock-Based Compensation Expense) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 27, 2012	Jan. 28, 2011	Jan. 27, 2012	Jan. 28, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 76.7	$ 45.0	$ 197.8	$ 127.0
Cost Of Product Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1.6	1.0	4.1	2.7
Cost Of Service Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	5.7	3.6	13.8	10.6
Sales And Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	37.5	21.3	96.5	59.2
Research And Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	22.8	11.3	57.0	31.6
General And Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 9.1	$ 7.8	$ 26.4	$ 22.9