Pension Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
United States
Change in benefit obligation:
Benefit obligation at beginning of year	$ 283.9	$ 275.6	$ 257.1
Participant contributions	0.1		0.1
Interest cost	4.3	6.8	9.5
Benefits and expenses paid	(18.5)	(18.4)	(17.6)
Actuarial (gain) loss	(3.7)	22.0	27.8
Plan settlements	(0.7)	(2.1)	(1.3)
Benefit obligation at end of year	265.4	283.9	275.6
International
Change in benefit obligation:
Benefit obligation at beginning of year	1,440.3	1,311.3	1,188.8
Service cost	0.5	0.6	0.5
Participant contributions	0.3	0.3	0.3
Interest cost	21.6	22.4	29.7
Benefits and expenses paid	(48.6)	(42.9)	(41.3)
Actuarial (gain) loss	(4.7)	82.8	206.5
Plan settlements	(5.9)	(4.1)	(3.7)
Plan amendments	0.4		5.2
Foreign currency translation (gain) loss	66.9	69.9	(74.7)
Benefit obligation at end of year	$ 1,470.8	$ 1,440.3	$ 1,311.3