Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended		9 Months Ended
	Nov. 25, 2022	Aug. 11, 2022	Mar. 09, 2022	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Class of Stock [Line Items]
Total share repurchase cost						$ 117.6	$ 20.5
Common Class A | Common Stock
Class of Stock [Line Items]
Shares repurchased (in millions)							0.8
Average price per share							$ 23.34
Total share repurchase cost							$ 18.1
Treasury Stock, Shares, Cancelled			0.8
BellRing Common Stock | Common Stock
Class of Stock [Line Items]
Shares repurchased (in millions)	0.9	0.8		1.3	0.1	4.0	0.1
Average price per share				$ 36.13	$ 22.94	$ 29.08	$ 22.94
Total share repurchase cost				$ 49.5	$ 2.4	$ 118.3	$ 2.4
Excise Tax Payable, Current				$ 0.7		$ 0.7