Long Term Debt - Joinder Agreements (Details) - USD ($) shares in Millions, $ in Millions			12 Months Ended
	Nov. 25, 2022	Aug. 11, 2022	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Nov. 18, 2022
Debt Instrument
Gross Repayments of Long-term debt			$ 2,049.5	$ 349.8	$ 1,661.1
Gross Exchanges of Long-term debt			0.0	99.9	1,182.3
Post \| BellRing
Debt Instrument
Noncontrolling Interest, Common Stock, Transfer	4.6	14.8
Incremental Term Loan \| Term Loan
Debt Instrument
Gross Repayments of Long-term debt					840.0
5.75% Senior Notes Maturing March 2027 \| Senior Notes
Debt Instrument
Gross Repayments of Long-term debt			459.3		$ 840.0
Debt Instrument, Redemption Price, Percentage					102.875%
Gross Exchanges of Long-term debt			$ 0.0		$ 0.0
Second Incremental Term Loan \| Term Loan
Debt Instrument
Gross Repayments of Long-term debt					107.7
Loans Payable to Bank					450.0
Gross Exchanges of Long-term debt					342.3
Third Incremental Term Loan \| Term Loan
Debt Instrument
Gross Repayments of Long-term debt				30.1
Loans Payable to Bank						$ 130.0
Gross Exchanges of Long-term debt				$ 99.9
First Incremental Term Loan \| Term Loan
Debt Instrument
Gross Repayments of Long-term debt					0.0
Gross Exchanges of Long-term debt					$ 840.0