Earnings Per Share (Policies)	12 Months Ended
Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings Per Share, Policy	Basic earnings per share is based on the average number of shares of Class A Common Stock outstanding during the period. Diluted earnings per share is based on the average number of shares of Class A Common Stock used for the basic earnings per share calculation, adjusted for the dilutive effect of stock options and restricted stock units using the “treasury stock” method. In addition, “Net earnings available to Class A Common Stockholders for diluted earnings per share” in the table below has been adjusted for diluted net earnings per share attributable to NCI, to the extent it is dilutive.BellRing Inc.’s Class B Common Stock does not have economic rights, including rights to dividends or distributions upon liquidation, and is therefore not a participating security. As such, separate presentation of basic and diluted earnings per share of Class B Common Stock under the two-class method has not been presented.

Disclosure of accounting policy for computing basic and diluted earnings or loss per share for each class of common stock and participating security. Addresses all significant policy factors, including any antidilutive items that have been excluded from the computation and takes into account stock dividends, splits and reverse splits that occur after the balance sheet date of the latest reporting period but before the issuance of the financial statements.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3630-109257

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