Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Deferred income tax assets:
Compensation and benefits	$ 6.0	$ 6.0
Inventory	10.5	11.1
Returns, rebates and incentives	34.5	29.8
Retirement benefits	306.8	298.5
Environmental remediation and other site-related costs	23.8	26.2
Share-based compensation	18.6	21.6
Other accruals and reserves	68.4	46.9
Investments	31.6	69.6
Net operating loss carryforwards	31.1	18.5
Tax credit carryforwards	17.3	16.5
Capital loss carryforwards	10.8	9.5
Other	16.8	10.7
Subtotal	576.2	564.9
Valuation allowance	(58.0)	(93.8)
Net deferred income tax assets	518.2	471.1
Deferred income tax liabilities:
Property	(48.0)	(55.8)
Intangible assets	(25.3)	(24.4)
Unremitted earnings of foreign subsidiaries	(28.3)	(25.5)
Other	(1.0)	(1.3)
Deferred income tax liabilities	(102.6)	(107.0)
Total net deferred income tax assets	$ 415.6	$ 364.1