Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Class of Stock [Line Items]
Total share repurchase cost (b)			$ 106.1	$ 117.6
BellRing Common Stock | Common Stock
Class of Stock [Line Items]
Shares repurchased	1.3	1.3	1.9	4.0
Average price per share	$ 58.08	$ 36.13	$ 56.18	$ 29.08
Total share repurchase cost (b)	$ 74.6	$ 49.5	$ 107.1	$ 118.3
Excise Tax Payable, Current	$ 1.0	$ 0.7	$ 1.0	$ 0.7