Employee Stock Plans - Summary the Effect of Recording Pre-Tax Share-Based Compensation Expense for Equity Incentive Awards (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 46.4	$ 39.2	$ 42.2
Equity Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	10.3	9.2	9.9
Restricted Stock Units and Restricted Stock Awards
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	31.9	26.2	28.7
Employee Stock Purchase Plans
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 4.2	$ 3.8	$ 3.6