Accumulated Other Comprehensive Income (Loss) - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) on Condensed Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Prior Service Costs
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ 0.2	$ 0.1	$ 0.4	$ 0.3
Actuarial (Gains) Losses
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1.2	0.8	2.5	1.5
Employee Pension and Postretirement Benefits, Net of Tax
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1.4	0.9	2.9	1.8
Tax benefit	(0.2)	(0.2)	(0.5)	(0.4)
Net of tax	$ 1.2	$ 0.7	$ 2.4	$ 1.4