Summary of Significant Accounting Policies - Intangibles (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Finite-Lived and Indefinite-Lived, Intangible Assets [Line Items]
Amortization of intangible assets	$ 17.0	$ 35.0	$ 26.6
Amortization of intangible assets, next twelve months	17.0
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		17.4	$ 7.1
Intangible Assets, Net
Finite-lived intangible assets, gross	328.4	328.2
Finite-Lived Intangible Assets, Accumulated Amortization	(203.4)	(186.4)
Finite-Lived Intangible Assets, Net	125.0	141.8
Customer relationships
Intangible Assets, Net
Finite-lived intangible assets, gross	160.8	160.7
Finite-Lived Intangible Assets, Accumulated Amortization	(103.4)	(94.6)
Finite-Lived Intangible Assets, Net	57.4	66.1
Trademarks and brands
Intangible Assets, Net
Finite-lived intangible assets, gross	164.5	164.4
Finite-Lived Intangible Assets, Accumulated Amortization	(96.9)	(88.7)
Finite-Lived Intangible Assets, Net	67.6	75.7
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