v3.20.4
Noncontrolling Interests, Equity Interests and Related Party Transactions (Details)
$ / shares in Units, shares in Millions, $ in Millions
 3 Months Ended
Oct. 21, 2019
USD ($)
$ / shares
shares
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Sep. 30, 2020
USD ($)
Oct. 01, 2018
USD ($)
Schedule of Equity Method Investments          
Proceeds from initial public offering   $ 0.0 $ 524.4    
Equity method earnings (loss), net of tax   (7.9) (7.3)    
Equity method investments   $ 106.8   $ 114.1  
Number of Joint Ventures Held   2      
8th Avenue          
Schedule of Equity Method Investments          
Net Loss Available to 8th Avenue Common Shareholders   $ (10.2) $ (8.7)    
Equity Method Investment, Ownership Percentage   60.50% 60.50%    
Equity method loss available to Common Shareholders   $ (6.2) $ (5.3)    
Amortization of basis difference, net of tax   1.7 1.7    
Equity method earnings (loss), net of tax   (7.9) (7.0)    
Total Basis Difference Recognized         $ 70.3
Remaining Basis Difference to be Amortized   52.9   54.6  
Net sales   229.0 218.4    
Gross profit   35.4 38.4    
Net loss   (1.4) (0.9)    
Less: Preferred stock dividend   8.8 7.8    
Revenue from Related Parties   2.0 1.6    
Purchases from and Royalties paid to Related Party   $ 2.2 2.8    
Alpen Food Company South Africa (Pty) Limited          
Schedule of Equity Method Investments          
Equity Method Investment, Ownership Percentage   50.00%      
Equity method earnings (loss), net of tax   $ 0.0 (0.3)    
Equity Method Investments | 8th Avenue          
Schedule of Equity Method Investments          
Equity method investments   102.2   110.1  
Equity Method Investments | Alpen Food Company South Africa (Pty) Limited          
Schedule of Equity Method Investments          
Equity method investments   4.6   4.0  
Accounts Receivable | 8th Avenue          
Schedule of Equity Method Investments          
Accounts Receivable, Related Parties   4.6   3.2  
Accounts Payable | 8th Avenue          
Schedule of Equity Method Investments          
Accounts Payable, Related Parties   0.6   0.6  
Other Liabilities | 8th Avenue          
Schedule of Equity Method Investments          
Due to Related Parties   0.7   0.7  
Other Assets | Alpen Food Company South Africa (Pty) Limited          
Schedule of Equity Method Investments          
Notes Receivable, Related Parties, Noncurrent   0.5   $ 0.5  
Selling, General and Administrative Expenses | 8th Avenue          
Schedule of Equity Method Investments          
MSA and Advisory Income   $ 0.8 1.0    
BellRing Brands, LLC | BellRing Brands, Inc.          
Schedule of Equity Method Investments          
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 28.80% 28.80%   28.80%  
BellRing Brands, LLC | Post Holdings, Inc.          
Schedule of Equity Method Investments          
Noncontrolling Interest, Ownership Percentage by Parent 71.20% 71.20%   71.20%  
Post Holdings, Inc. | Weetabix East Africa Limited          
Schedule of Equity Method Investments          
Noncontrolling Interest, Ownership Percentage by Parent   50.10%      
Additional Paid-in Capital          
Schedule of Equity Method Investments          
Net transfers from noncontrolling interest   $ 0.0 457.0    
Additional Paid-in Capital | BellRing          
Schedule of Equity Method Investments          
Proceeds from initial public offering   0.0 524.4    
Increase in additional paid-in capital related to establishment of noncontrolling interest   0.0 66.3    
Decrease in additional paid-in capital related to tax effects of IPO   0.0 (133.7)    
Net transfers from noncontrolling interest   $ 0.0 $ 457.0    
Minimum | BellRing Brands, LLC | Post Holdings, Inc.          
Schedule of Equity Method Investments          
Noncontrolling Interest, Ownership Percentage by Parent 50.00%        
Common Class A | BellRing Brands, Inc.          
Schedule of Equity Method Investments          
Common Stock, Shares, Issued | shares 39.4        
Common Stock, Par or Stated Value Per Share | $ / shares $ 0.01        
Proceeds from initial public offering $ 524.4        
Common Class B | BellRing Brands, Inc.          
Schedule of Equity Method Investments          
Common Stock, Par or Stated Value Per Share | $ / shares $ 0.01        
Initial Public Offering, Percentage of Voting Interests 67.00%