Intangible Assets, Goodwill, Acquisitions and Divestitures - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 701.4	$ 672.8
Accumulated Amortization	(503.8)	(451.5)
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	694.9	666.3
Accumulated Amortization	$ (499.8)	(448.3)
Customer Relationships | Minimum
Finite Lived Intangible Assets [Line Items]
Useful Life	6 years
Customer Relationships | Maximum
Finite Lived Intangible Assets [Line Items]
Useful Life	21 years
Trademarks
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3.8	3.8
Accumulated Amortization	$ (2.3)	(2.0)
Trademarks | Minimum
Finite Lived Intangible Assets [Line Items]
Useful Life	4 years
Trademarks | Maximum
Finite Lived Intangible Assets [Line Items]
Useful Life	12 years
Noncompete Agreements
Finite Lived Intangible Assets [Line Items]
Useful Life	5 years
Gross Carrying Amount	$ 2.7	2.7
Accumulated Amortization	$ (1.7)	$ (1.2)