Intangible Assets, Goodwill and Acquisitions - Summary of Goodwill (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Mar. 31, 2023	Sep. 30, 2022
Goodwill [Line Items]
Beginning balance		$ 2,008.8	$ 1,950.8
Acquisitions	[1]	14.6	58.0
Ending balance		2,023.4	2,008.8
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,792.7	1,758.0
Acquisitions	[1]	12.0	34.7
Ending balance		1,804.7	1,792.7
Development Services
Goodwill [Line Items]
Beginning balance		216.1	192.8
Acquisitions	[1]	2.6	23.3
Ending balance		$ 218.7	$ 216.1

[1] The acquisitions adjustment includes the immaterial impact of foreign currency adjustments during the period