Pension Plans - Schedule of Net Benefit Costs (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.0	$ 0.0
Interest cost	3.2	4.0
Expected return on plan assets	(5.5)	(6.1)
Amortization of unrecognized net losses	1.8	1.6
Net periodic (benefit)/cost	(0.5)	(0.5)
International
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.2
Interest cost	0.4	0.3
Expected return on plan assets	(0.8)	(0.6)
Amortization of unrecognized net losses	0.4	0.3
Net periodic (benefit)/cost	$ 0.2	$ 0.2