| Cover Page - USD ($) | 12 Months Ended | ||
| Sep. 30, 2020 | Nov. 16, 2020 | Mar. 31, 2020 | |
| Document Information [Line Items] | |||
| Document Type | 10-K/A | ||
| Document Annual Report | true | ||
| Document Period End Date | Sep. 30, 2020 | ||
| Document Fiscal Year Focus | 2020 | ||
| Document Fiscal Period Focus | FY | ||
| Current Fiscal Year End Date | --09-30 | ||
| Document Transition Report | false | ||
| Amendment Flag | true | ||
| Amendment Description | BellRing Brands, Inc. (the “Company,” “we,” “us,” and “our”) is filing this Amendment No. 1 (the “Amendment”) on Form 10-K/A to amend our Annual Report on Form 10-K for the fiscal year ended September 30, 2020, filed with the U.S. Securities and Exchange Commission on November 20, 2020 (the “Original 10-K”), for the purpose of filing revised versions of Exhibits 31.1, 31.2 and 31.3 filed with the Original 10-K. | ||
| Entity File Number | 1-39093 | ||
| Entity Registrant Name | BellRing Brands, Inc. | ||
| Entity Incorporation, State or Country Code | DE | ||
| Entity Tax Identification Number | 83-4096323 | ||
| Entity Central Index Key | 0001772016 | ||
| Entity Address, Address Line One | 2503 S. Hanley Road | ||
| Entity Address, City or Town | St. Louis | ||
| Entity Address, State or Province | MO | ||
| Entity Address, Postal Zip Code | 63144 | ||
| City Area Code | 314 | ||
| Local Phone Number | 644-7600 | ||
| Title of 12(b) Security | Class A Common Stock, $0.01 par value | ||
| Trading Symbol | BRBR | ||
| Security Exchange Name | NYSE | ||
| Entity Well-known Seasoned Issuer | Yes | ||
| Entity Voluntary Filers | No | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Filer Category | Non-accelerated Filer | ||
| Entity Small Business | false | ||
| Entity Emerging Growth Company | true | ||
| Entity Ex Transition Period | true | ||
| ICFR Auditor Attestation Flag | false | ||
| Entity Shell Company | false | ||
| Entity Public Float | $ 672,257,136 | ||
| Documents Incorporated by Reference | Certain portions of the registrant’s definitive proxy statement for its 2021 annual meeting of stockholders, to be filed with the Securities and Exchange Commission within 120 days after September 30, 2020, are incorporated by reference into Part III of this report. | ||
| Common Class A | |||
| Document Information [Line Items] | |||
| Entity Common Stock, Shares Outstanding | 39,428,571 | ||
| Common Class B | |||
| Document Information [Line Items] | |||
| Entity Common Stock, Shares Outstanding | 1 |
