Accumulated Other Comprehensive Income - Schedule of Reclassifications From Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension and other postretirement benefit plan remeasurement (gain) loss	$ 6.9	$ (128.2)	$ (54.9)
(Gain) loss on liquidation of subsidiary	(9.1)	(8.1)	(6.4)
Income tax expense (benefit)	34.7	59.9	53.4
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension and other postretirement benefit plan remeasurement (gain) loss	(2.2)	(11.8)	(11.8)
(Gain) loss on liquidation of subsidiary	0.0	0.0	0.6
Gain (loss) on hedging activity	(1.4)	0.7	0.0
Income tax expense (benefit)	(3.4)	2.1	3.0
Other comprehensive income (loss), net of tax	$ (4.2)	$ (10.4)	$ (8.2)