Retirement and Other Benefit Plans - Schedule Of Reconciliation Of Benefit Obligation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Retirement and Other Benefit Plans
Net benefit obligation at beginning of year	$ 100.1	$ 89.8
Interest cost	3.0	3.7	$ 3.4
Actuarial loss	6.9	11.3
Gross benefits paid	(4.8)	(4.7)
Settlements	(102.4)	0.0
Net benefit obligation at end of year	$ 2.8	$ 100.1	$ 89.8