Intangible Assets, Goodwill, Acquisitions and Divestitures - Summary of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Goodwill [Line Items]
Beginning balance		$ 1,810.4	$ 1,766.8
Acquisitions		64.4	43.6
Impairment Loss	$ (15.5)	(15.5)
Ending balance	1,859.3	1,859.3	1,810.4
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,616.0	1,572.4
Acquisitions		64.4	43.6
Ending balance	1,680.4	1,680.4	1,616.0
Development Services
Goodwill [Line Items]
Beginning balance		194.4	194.4
Impairment Loss		(15.5)
Ending balance	$ 178.9	$ 178.9	$ 194.4

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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