Restructuring Charges - Charges Taken Related to Accrued Restructuring Actions (Detail) $ in Millions	3 Months Ended
	Dec. 30, 2017 USD ($)
Restructuring Reserve [Roll Forward]
Stock-based compensation	$ (1.3)
Restructuring | Two Thousand Seventeen [Member]
Restructuring Reserve [Roll Forward]
Period beginning balance	11.5
Restructuring | Two Thousand Seventeen [Member] | Fiscal 2018 Action [Member]
Restructuring Reserve [Roll Forward]
Period beginning balance	0.0
Restructuring | Two Thousand Seventeen [Member] | Fiscal 2017 Actions [Member]
Restructuring Reserve [Roll Forward]
Period beginning balance	7.5
Restructuring | Two Thousand Seventeen [Member] | Fiscal 2016 Actions
Restructuring Reserve [Roll Forward]
Period beginning balance	3.7
Restructuring | Two Thousand Seventeen [Member] | Other Restructuring [Member]
Restructuring Reserve [Roll Forward]
Period beginning balance	0.3
Restructuring | Two thousand eighteen [Member]
Restructuring Reserve [Roll Forward]
Fiscal 2018 charges	3.8
Severance payments and adjustments	(3.4)
Other payments	(0.4)
Period end balance	10.2
Restructuring | Two thousand eighteen [Member] | Fiscal 2018 Action [Member]
Restructuring Reserve [Roll Forward]
Fiscal 2018 charges	3.8
Stock-based compensation	(1.3)
Severance payments and adjustments	(0.9)
Other payments	0.0
Period end balance	1.6
Restructuring | Two thousand eighteen [Member] | Fiscal 2017 Actions [Member]
Restructuring Reserve [Roll Forward]
Fiscal 2018 charges	0.0
Stock-based compensation	0.0
Severance payments and adjustments	(2.3)
Other payments	0.0
Period end balance	5.2
Restructuring | Two thousand eighteen [Member] | Fiscal 2016 Actions
Restructuring Reserve [Roll Forward]
Fiscal 2018 charges	0.0
Stock-based compensation	0.0
Severance payments and adjustments	(0.2)
Other payments	(0.3)
Period end balance	3.2
Restructuring | Two thousand eighteen [Member] | Other Restructuring [Member]
Restructuring Reserve [Roll Forward]
Fiscal 2018 charges	0.0
Stock-based compensation	0.0
Severance payments and adjustments	0.0
Other payments	(0.1)
Period end balance	$ 0.2