Pension Benefit Obligations - Periodic Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Plan, Defined Benefit
Components of net periodic benefit cost:
Applicable deferred income taxes, included in OCI arising from net prior service cost and net gain/loss	$ 15.0	$ 15.9	$ 15.8
United States
Components of net periodic benefit cost:
Interest cost on projected benefit obligation	6.4	8.6	7.4
Expected return on plan assets	(7.0)	(9.0)	(9.0)
Amortization of prior service costs (credits)	0.1	0.1	0.1
Amortization of net loss	5.0	3.9	4.1
Curtailment loss recognized	0.5
Settlement loss recognized	0.6	0.2
Net periodic benefit cost	5.6	3.8	2.6
International
Components of net periodic benefit cost:
Service costs	0.6	0.5	1.1
Interest cost on projected benefit obligation	22.4	29.7	32.0
Expected return on plan assets	(37.5)	(38.1)	(43.1)
Amortization of prior service costs (credits)	0.1	(0.1)	(0.2)
Amortization of net loss	8.6	4.1	8.2
Settlement loss recognized	0.5	0.8	0.3
Net periodic benefit cost	$ (5.3)	$ (3.1)	$ (1.7)