Intangible Assets, Goodwill, Acquisitions and Divestitures - Summary of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Goodwill [Line Items]
Beginning balance		$ 1,859.3	$ 1,810.4
Acquisitions		91.5	64.4
Impairment Loss	$ (15.5)	0.0	(15.5)
Ending balance	1,859.3	1,950.8	1,859.3
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,680.4	1,616.0
Acquisitions		77.6	64.4
Impairment Loss			0.0
Ending balance	1,680.4	1,758.0	1,680.4
Development Services
Goodwill [Line Items]
Beginning balance		178.9	194.4
Acquisitions		13.9	0.0
Impairment Loss			(15.5)
Ending balance	$ 178.9	$ 192.8	$ 178.9

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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