Intangible Assets, Goodwill and Acquisitions - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Goodwill [Line Items]
Beginning balance	$ 1,766.8	$ 1,703.8
Acquisitions	43.6	63.0
Ending balance	1,810.4	1,766.8
Maintenance Services
Goodwill [Line Items]
Beginning balance	1,572.4	1,523.3
Acquisitions	43.6	49.1
Ending balance	1,616.0	1,572.4
Development Services
Goodwill [Line Items]
Beginning balance	194.4	180.5
Acquisitions		13.9
Ending balance	$ 194.4	$ 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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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