Valuation and Qualifying Accounts - Schedule II Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 29, 2017
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 41.1	$ 63.1	$ 24.2
Provision to Allowance for Doubtful Accounts	6.6	4.0	43.0
Write-offs Adjustments Charged to Allowance	(1.2)	(26.0)	(4.1)
Balance at End of Period	46.5	41.1	63.1
Valuation allowance for deferred tax assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	101.6	105.8	79.6
Increases	6.7	5.3	26.2
Deductions	(8.6)	(9.5)	0.0
Balance at End of Period	$ 99.7	$ 101.6	$ 105.8