Income Taxes - Activity of Company's Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 28, 2019	Sep. 29, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of fiscal year	$ 89.5	$ 90.3
Tax positions related to current year:
Additions	22.7	9.0
Reductions	0.0	0.0
Tax positions related to prior years:
Additions related to change in estimate	0.0	6.6
Reductions	(4.8)	(15.4)
Payments	0.0	0.0
Lapses in statutes of limitations	(5.8)	(1.4)
Acquired tax positions:
Additions related to reserves acquired from acquisitions	0.0	0.4
Balance as of the end of the fiscal year	$ 101.6	$ 89.5

Tax positions related to current year.

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Tax positions related to prior years.

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Unrecognized tax benefits increases.

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Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from acquisitions.

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