Pension Plans - Schedule of Net Benefit Costs (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Interest cost	3.2	3.2	6.4	6.4
Expected return on plan assets	(5.7)	(5.5)	(11.4)	(11.0)
Amortization of unrecognized net losses	1.6	1.8	3.2	3.6
Net periodic (benefit)/cost	(0.9)	(0.5)	(1.8)	(1.0)
International
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.2	0.4	0.4
Interest cost	0.4	0.4	0.9	0.8
Expected return on plan assets	(0.9)	(0.8)	(1.7)	(1.6)
Amortization of unrecognized net losses	0.3	0.4	0.4	0.8
Net periodic (benefit)/cost	$ 0.0	$ 0.2	$ 0.0	$ 0.4