Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended	6 Months Ended
	Nov. 25, 2022	Aug. 11, 2022	Mar. 09, 2022	Mar. 31, 2023	Mar. 31, 2023	Mar. 31, 2022
Class of Stock [Line Items]
Total share repurchase cost					$ 68.5	$ 18.1
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		0.9	2.7
Average price per share				$ 29.74	$ 25.52
Total share repurchase cost				$ 27.6	$ 68.8
Accrued Excise Tax				$ 0.3	$ 0.3