Restructuring Charges - Charges Taken Related to Accrued Restructuring Actions (Detail) $ in Millions	6 Months Ended
	Mar. 30, 2019 USD ($)
Fiscal 2018 charges
Restructuring Reserve [Roll Forward]
Balance as of September 29, 2018	$ 9.1
Fiscal 2018 charges | Fiscal 2019 Action [Member]
Restructuring Reserve [Roll Forward]
Balance as of September 29, 2018	0.0
Fiscal 2018 charges | Fiscal 2018 Actions
Restructuring Reserve [Roll Forward]
Balance as of September 29, 2018	4.3
Fiscal 2018 charges | Fiscal 2017 Actions
Restructuring Reserve [Roll Forward]
Balance as of September 29, 2018	0.8
Fiscal 2018 charges | Fiscal 2016 Actions
Restructuring Reserve [Roll Forward]
Balance as of September 29, 2018	3.9
Fiscal 2018 charges | Other
Restructuring Reserve [Roll Forward]
Balance as of September 29, 2018	0.1
Restructuring | Fiscal 2019 charges
Restructuring Reserve [Roll Forward]
Fiscal 2019 charges	3.3
Severance payments and adjustments	(6.0)
Other payments	(1.4)
Balance as of March 30, 2019	5.0
Restructuring | Fiscal 2019 charges | Fiscal 2019 Action [Member]
Restructuring Reserve [Roll Forward]
Fiscal 2019 charges	2.3
Severance payments and adjustments	(1.9)
Other payments	0.0
Balance as of March 30, 2019	0.4
Restructuring | Fiscal 2019 charges | Fiscal 2018 Actions
Restructuring Reserve [Roll Forward]
Fiscal 2019 charges	1.0
Severance payments and adjustments	(3.6)
Other payments	(0.5)
Balance as of March 30, 2019	1.2
Restructuring | Fiscal 2019 charges | Fiscal 2017 Actions
Restructuring Reserve [Roll Forward]
Fiscal 2019 charges	0.0
Severance payments and adjustments	(0.5)
Other payments	0.0
Balance as of March 30, 2019	0.3
Restructuring | Fiscal 2019 charges | Fiscal 2016 Actions
Restructuring Reserve [Roll Forward]
Fiscal 2019 charges	0.0
Severance payments and adjustments	0.0
Other payments	(0.9)
Balance as of March 30, 2019	3.0
Restructuring | Fiscal 2019 charges | Other
Restructuring Reserve [Roll Forward]
Fiscal 2019 charges	0.0
Severance payments and adjustments	0.0
Other payments	0.0
Balance as of March 30, 2019	$ 0.1