Valuation and Qualifying Accounts - Schedule II Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 63.1	$ 24.2	$ 21.1
Charged to Bad Debt Expense	4.0	43.0	3.4
Write-offs Adjustments Charged to Allowance	(26.0)	(4.1)	(0.3)
Balance at End of Period	41.1	63.1	24.2
Valuation allowance for deferred tax assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	105.8	79.6	69.7
Increases	5.3	26.2	12.2
Deductions	(9.5)	0.0	(2.3)
Balance at End of Period	$ 101.6	$ 105.8	$ 79.6