v3.24.2.u1
Goodwill (Details) - USD ($)
$ in Millions
 9 Months Ended
Jun. 30, 2024
Sep. 30, 2023
Goodwill    
Goodwill (gross) $ 5,348.7 $ 5,274.4
Accumulated impairment losses (700.0) (700.0)
Goodwill 4,648.7 4,574.4
Goodwill from acquisition 42.7  
Currency translation adjustment 31.6  
Post Consumer Brands    
Goodwill    
Goodwill (gross) 2,303.8 2,261.1
Accumulated impairment losses (609.1) (609.1)
Goodwill 1,694.7 1,652.0
Goodwill from acquisition 42.7  
Currency translation adjustment 0.0  
Weetabix    
Goodwill    
Goodwill (gross) 885.9 854.3
Accumulated impairment losses 0.0 0.0
Goodwill 885.9 854.3
Goodwill from acquisition 0.0  
Currency translation adjustment 31.6  
Foodservice    
Goodwill    
Goodwill (gross) 1,355.3 1,355.3
Accumulated impairment losses 0.0 0.0
Goodwill 1,355.3 1,355.3
Goodwill from acquisition 0.0  
Currency translation adjustment 0.0  
Refrigerated Retail    
Goodwill    
Goodwill (gross) 803.7 803.7
Accumulated impairment losses (90.9) (90.9)
Goodwill 712.8 $ 712.8
Goodwill from acquisition 0.0  
Currency translation adjustment $ 0.0