Intangible Assets, Goodwill and Acquisitions - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2022	Sep. 30, 2021
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 718.2	$ 701.4
Accumulated Amortization	529.2	503.8
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	711.7	694.9
Accumulated Amortization	$ 524.8	499.8
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	$ 2.5	2.3
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	$ 1.9	$ 1.7