Accumulated Other Comprehensive Income (Loss) - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) Included in Computation of Net Periodic Pension and Postretirement Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2022	Sep. 30, 2021	Sep. 30, 2020
Prior Service Costs
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ 0.2	$ 0.8	$ 0.9	$ 0.7
Settlement
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		33.6
Actuarial (Gains) Losses
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	0.3	1.3	5.2	3.1
Employee Pension and Postretirement Benefits, Net of Tax
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	0.5	35.7	6.1	3.8
Tax benefit	(0.1)	(8.3)	(1.5)	(1.0)
Net of tax	$ 0.4	$ 27.4	$ 4.6	$ 2.8