Intangible Assets, Goodwill and Acquisitions - Summary of Goodwill (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2023	Sep. 30, 2022
Goodwill [Line Items]
Beginning balance		$ 2,008.8	$ 1,950.8
Acquisitions	[1]	12.6	58.0
Ending balance		2,021.4	2,008.8
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,792.7	1,758.0
Acquisitions	[1]	10.7	34.7
Ending balance		1,803.4	1,792.7
Development Services
Goodwill [Line Items]
Beginning balance		216.1	192.8
Acquisitions	[1]	1.9	23.3
Ending balance		$ 218.0	$ 216.1

[1] The acquisitions adjustments include the immaterial impact of foreign currency and other prior year measurement period adjustments during the respective periods.