Stockholders' Equity (Details) - Common Stock - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Class of Stock [Line Items]
Purchases of treasury stock, shares	(2.6)	(4.2)	(1.9)
Common Class A
Class of Stock [Line Items]
Purchases of treasury stock, shares			0.8
Treasury Stock Acquired, Average Cost Per Share			$ 23.34
Payments for Repurchase of Common Stock			$ 18.1
BellRing Common Stock
Class of Stock [Line Items]
Purchases of treasury stock, shares	2.6	4.2	1.1
Treasury Stock Acquired, Average Cost Per Share	$ 56.12	$ 29.56	$ 23.17
Payments for Repurchase of Common Stock	$ 148.0	$ 126.3	$ 24.7
Sales and Excise Tax Payable, Current	$ 1.4	$ 0.8