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Net earnings attributable to redeemable noncontrolling interest subsequent to IPO

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Voting power of common stock for so long as Post Holdings, Inc. or its affiliates (other than the Company) directly own more than 50% of the BellRing LLC units

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Face amount or stated value per share of common stock.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Number of common units of ownership outstanding of a limited liability company (LLC).

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Oct. 21, 2019
Net earnings attributable to redeemable noncontrolling interest	$ 25.1	$ 25.8
Net earnings attributable to NCI prior to IPO	0.0	5.5
Net earnings attributable to NCI after IPO	25.1	20.3
Proceeds from issuance of common stock, net of issuance costs	$ 0.0	$ 524.4
Common Class A
Common stock, shares issued				39,400,000
Common stock, par value per share	$ 0.01
Voting power of common stock	33.00%
Common stock, shares outstanding	39,500,000
Common Class B
Common stock, par value per share	$ 0.01
Voting power of common stock	67.00%
Common stock, shares outstanding	1
BellRing Brands, LLC unit \| BellRing Brands, Inc.
Common unit, issued				39,400,000
Noncontrolling interest, ownership percentage by parent	28.80%		28.80%
BellRing Brands, LLC unit \| Post Holdings, Inc.
Noncontrolling interest, ownership percentage by noncontrolling owners	71.20%		71.20%	100.00%
Common units, outstanding	97,500,000		97,500,000