Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Related Party Transaction [Line Items]
Selling, general and administrative expenses	$ 284.6	$ 216.3	$ 189.7
Purchases from related party	8.6
Accounts payable	121.0	89.0
Master services agreement fees
Related Party Transaction [Line Items]
Selling, general and administrative expenses	3.4	4.0	$ 4.6
Post Holdings, Inc. \| Accounts payable
Related Party Transaction [Line Items]
Accounts payable	$ 1.5	$ 2.5

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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- Definition

The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc.

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