Intangible Assets, Goodwill and Acquisitions - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 664.4	$ 647.1
Accumulated Amortization	(422.7)	(395.6)
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	656.9	639.6
Accumulated Amortization	$ (420.0)	(393.3)
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	$ 4.8	4.8
Accumulated Amortization	$ (1.8)	(1.7)
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	$ (0.9)	$ (0.6)
Noncompete Agreements | Minimum
Finite Lived Intangible Assets [Line Items]
Useful Life	5 years