Stockholders' Equity (Details) - Common Stock - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Class of Stock [Line Items]
Purchases of treasury stock, shares	(9.0)	(2.6)	(4.2)
Payments for Other Taxes	$ 2.2
BellRing Common Stock
Class of Stock [Line Items]
Purchases of treasury stock, shares	9.0	2.6	4.2
Treasury Stock Acquired, Average Cost Per Share	$ 52.62	$ 56.12	$ 29.56
Payments for Repurchase of Common Stock	$ 476.6	$ 148.0	$ 126.3
Sales and Excise Tax Payable, Current	$ 3.9	$ 1.4	$ 0.8