Other Financial Information - Other Assets (Detail) - USD ($) $ in Millions	Sep. 27, 2019	Sep. 28, 2018
Other Financial Information [Abstract]
Long-term receivables	$ 74.3	$ 71.7
Deferred Compensation Plan (DCP) assets	79.0	75.2
Equity investments	64.2	39.4
Long-term available-for-sale securities	58.2	23.1
California Proton Therapy Center (CPTC) Term loan	44.0	44.0
RPTC senior secured debt	23.5	0.0
Other	54.0	39.4
Total other assets	$ 397.2	$ 292.8