Intangible Assets, Goodwill and Acquisitions - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019
Goodwill [Line Items]
Beginning balance	$ 1,810.4	$ 1,766.8
Acquisitions	12.6	43.6
Ending balance	1,823.0	1,810.4
Maintenance Services
Goodwill [Line Items]
Beginning balance	1,616.0	1,572.4
Acquisitions	12.6	43.6
Ending balance	1,628.6	1,616.0
Development Services
Goodwill [Line Items]
Beginning balance	194.4	194.4
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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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