Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Class of Stock [Line Items]
Total share repurchase cost (b)			$ 30.8	$ 68.5
BellRing Common Stock | Common Stock
Class of Stock [Line Items]
Shares repurchased	0.4	0.9	0.6	2.7
Average price per share	$ 56.46	$ 29.74	$ 52.28	$ 25.52
Total share repurchase cost (b)	$ 23.1	$ 27.6	$ 32.5	$ 68.8
Payments of accrued repurchases of common stock	1.5		1.5
Excise Tax Payable, Current	$ 0.2		$ 0.2