Special Purpose Entities - Schedule of Restricted Assets and Non-recourse Liabilities Held by Special Purposes Entities (Details) - Rock-Tenn Company and MeadWestvaco Corporation's [Member] - Installment Note [Member] - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Debt Instrument [Line Items]
Other current assets	$ 867.9
Other noncurrent assets	381.1	$ 1,253.0
Other current liabilities	782.5
Other noncurrent liabilities	$ 330.2	$ 1,117.8