Intangible Assets, Goodwill, Acquisitions, and Divestitures - Summary of Goodwill (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Mar. 31, 2024	Sep. 30, 2023
Goodwill [Line Items]
Beginning balance		$ 2,021.4	$ 2,008.8
Acquisitions	[1]	0.1	12.6
Divestiture		(5.8)
Ending balance		2,015.7	2,021.4
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,803.4	1,792.7
Acquisitions	[1]	0.1	10.7
Divestiture		(5.8)
Ending balance		1,797.7	1,803.4
Development Services
Goodwill [Line Items]
Beginning balance		218.0	216.1
Acquisitions	[1]	0.0	1.9
Divestiture		0.0
Ending balance		$ 218.0	$ 218.0

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