Summary of Significant Accounting Policies - Intangibles (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Finite-Lived and Indefinite-Lived, Intangible Assets [Line Items]
Amortization of intangible assets	$ 26.6	$ 19.7	$ 51.2
Amortization of intangible assets, next twelve months	35.0
Amortization of intangible assets, year two	17.0
Amortization of intangible assets, year three	17.0
Amortization of intangible assets, year four	17.0
Amortization of intangible assets, year five	17.0
Accelerated amortization	7.1		$ 29.9
Intangible Assets, Net
Finite-lived intangible assets, gross	375.5	376.5
Finite-Lived Intangible Assets, Accumulated Amortization	(198.7)	(173.2)
Finite-Lived Intangible Assets, Net	176.8	203.3
Customer relationships
Intangible Assets, Net
Finite-lived intangible assets, gross	178.4	178.3
Finite-Lived Intangible Assets, Accumulated Amortization	(97.2)	(84.9)
Finite-Lived Intangible Assets, Net	81.2	93.4
Customer relationships | PowerBar brand
Intangible Assets, Net
Finite-Lived Intangible Assets, Net	6.4
Trademarks
Intangible Assets, Net
Finite-lived intangible assets, gross	194.0	195.1
Finite-Lived Intangible Assets, Accumulated Amortization	(98.4)	(85.2)
Finite-Lived Intangible Assets, Net	95.6	109.9
Trademarks | PowerBar brand
Intangible Assets, Net
Finite-Lived Intangible Assets, Net	11.6
Other intangible assets
Intangible Assets, Net
Finite-lived intangible assets, gross	3.1	3.1
Finite-Lived Intangible Assets, Accumulated Amortization	(3.1)	(3.1)
Finite-Lived Intangible Assets, Net	$ 0.0	$ 0.0