Pension and Other Employee Benefits - Schedule of Reconciliation of Benefit Obligations, Plan Assets Funded Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Other Liabilities Disclosure [Abstract]
Benefit obligation at beginning of year	$ (11.0)	$ (10.0)	$ (10.3)
Service cost	0.0	0.0	0.0
Interest cost	(0.1)	(0.2)	(0.3)
Plan participants’ contributions	0.0	0.0	0.0
Actuarial gain (loss)	1.5	(1.2)	(0.9)
Foreign exchange gain	(0.6)	0.1	1.2
Benefits paid	0.3	0.3	0.3
Benefit obligation at end of year	(9.9)	(11.0)	(10.0)
Plan assets	0.0	0.0	0.0
Benefit obligation at end of year	$ (9.9)	$ (11.0)	$ (10.0)