Intangible Assets, Goodwill and Acquisitions - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 689.3	$ 672.8
Accumulated Amortization	(465.4)	(451.5)
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	682.8	666.3
Accumulated Amortization	$ (462.0)	(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	$ (2.1)	(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]
Gross Carrying Amount	$ 2.7	2.7
Accumulated Amortization	$ (1.3)	$ (1.2)
Noncompete Agreements | Minimum
Finite Lived Intangible Assets [Line Items]
Useful Life	5 years