Summary of Significant Accounting Policies - Intangibles (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Finite-Lived and Indefinite-Lived, Intangible Assets [Line Items]
Amortization of intangible assets	$ 22.2	$ 22.2	$ 22.8
Amortization of intangible assets, next twelve months	22.2
Amortization of intangible assets, year two	22.2
Amortization of intangible assets, year three	22.2
Amortization of intangible assets, year four	22.2
Amortization of intangible assets, year five	22.2
Intangible Assets, Net
Finite-lived intangible assets, gross	425.9	425.9
Finite-Lived Intangible Assets, Accumulated Amortization	(151.6)	(129.4)
Finite-lived intangible assets, net	274.3	296.5
Customer relationships
Intangible Assets, Net
Finite-lived intangible assets, gross	209.4	209.4
Finite-Lived Intangible Assets, Accumulated Amortization	(76.9)	(65.5)
Finite-lived intangible assets, net	132.5	143.9
Trademarks
Intangible Assets, Net
Finite-lived intangible assets, gross	213.4	213.4
Finite-Lived Intangible Assets, Accumulated Amortization	(71.6)	(60.8)
Finite-lived intangible assets, net	141.8	152.6
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