Intangible Assets, Goodwill and Acquisitions - Summary of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Sep. 30, 2020	Mar. 31, 2021	Sep. 30, 2020
Goodwill [Line Items]
Beginning balance		$ 1,859.3	$ 1,810.4
Acquisitions		60.3	64.4
Impairment Loss	$ (15.5)		(15.5)
Ending balance	1,859.3	1,919.6	1,859.3
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,680.4	1,616.0
Acquisitions		50.8	64.4
Ending balance	1,680.4	1,731.2	1,680.4
Development Services
Goodwill [Line Items]
Beginning balance		178.9	194.4
Acquisitions		9.5
Impairment Loss			(15.5)
Ending balance	$ 178.9	$ 188.4	$ 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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