Stockholders' Equity (Details) - Common Stock - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Sep. 30, 2024
Class of Stock [Line Items]
Shares repurchased	0.1	0.2
Average price per share	$ 77.12	$ 44.27
Purchases of treasury stock	$ 11.0	$ 9.4
BellRing Common Stock
Class of Stock [Line Items]
Excise Tax Payable, Current			$ 0.8