Discontinued Operations - Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest and other financing expenses	$ 13.6	$ 18.7
Income tax expense (benefit)	11.9	(20.1)
(Loss) income from discontinued operations, net of tax	(2.0)	54.9
Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net revenues	0.0	705.8
Cost of sales	0.0	556.6
Gross profit	0.0	149.2
Selling, general and administrative expenses	0.0	72.3
Net legacy and separation-related expenses	2.3	6.2
Equity and other income, net	0.0	(9.2)
Operating (loss) income from discontinued operations	(2.3)	79.9
Net pension and other postretirement plan expense	0.0	0.1
Net interest and other financing expenses	0.0	2.3
(Loss) income before income taxes - discontinued operations	(2.3)	77.5
Income tax expense (benefit)	(0.3)	22.6
(Loss) income from discontinued operations, net of tax	$ (2.0)	$ 54.9