Employee Stock Plans - Net Share-Based Compensation Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Oct. 02, 2015	Sep. 26, 2014
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 48.3	$ 46.3	$ 39.6
Income tax benefit for share-based compensation	(14.8)	(14.2)	(12.1)
Cost of revenues - Product
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	4.2	4.7	3.3
Cost of revenues - Service
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	4.2	4.1	4.7
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	6.7	6.8	6.2
Selling, general and administrative expenses
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 33.2	$ 30.7	$ 25.4