Accrued Expenses and Other Long-Term Liabilities - Schedule of Other Long-Term Liabilities (Detail) - USD ($) $ in Millions	Sep. 26, 2020	Sep. 28, 2019
Other Long-Term Liabilities
Reserve for income tax uncertainties	$ 103.7	$ 106.8
Contingent consideration	81.8	0.0
Operating lease liabilities (non-current)	65.6	0.0
Interest rate swap	23.0	0.0
Accrued lease obligation—long-term	0.0	33.7
Pension liabilities	11.1	10.2
Other	18.0	11.7
Other long-term liabilities	$ 303.2	$ 162.4