Income Taxes (Details)	3 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Income Tax Disclosure
Effective income tax rate	6.00%	15.60%
BellRing Brands, LLC unit \| BellRing Brands, Inc.
Income Tax Disclosure
Noncontrolling interest, ownership percentage by parent	28.80%		28.80%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration