Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-Lived License Agreements	$ 2.7	$ 2.7
Indefinite-lived Intangible Assets (Excluding Goodwill)	4.8	4.8
Finite-Lived Intangible Assets, Accumulated Amortization	(16.2)	(15.5)
Finite-Lived Intangible Assets, Net	11.2	11.9
Other Indefinite-lived Intangible Assets	2.1	2.1
Finite-Lived Intangible Assets, Gross	27.4	27.4
Gross Finite and Indefinite-Lived Intangible Assets	32.2	32.2
Finite and Indefinited-Lived Accumulated Amortization and Impairment Charges	(16.2)	(15.5)
Intangible Assets, Net (Excluding Goodwill)	16.0	16.7
Computer Software, Intangible Asset [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Computer Software, Gross	5.3	5.3
Finite-Lived Intangible Assets, Accumulated Amortization	(3.1)	(3.0)
Finite-Lived Intangible Assets, Net	2.2	2.3
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Lists, Gross	22.1	22.1
Finite-Lived Intangible Assets, Accumulated Amortization	(13.1)	(12.5)
Finite-Lived Intangible Assets, Net	$ 9.0	$ 9.6