Intangible Assets, Goodwill and Acquisitions - Summary of Goodwill (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2023	Sep. 30, 2023
Goodwill [Line Items]
Beginning balance		$ 2,021.4	$ 2,008.8
Acquisitions	[1]	0.1	12.6
Ending balance		2,021.5	2,021.4
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,803.4	1,792.7
Acquisitions	[1]	0.1	10.7
Ending balance		1,803.5	1,803.4
Development Services
Goodwill [Line Items]
Beginning balance		218.0	216.1
Acquisitions	[1]	0.0	1.9
Ending balance		$ 218.0	$ 218.0

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