Intangible Assets, Goodwill, Acquisitions, and Divestitures - Summary of Goodwill (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Mar. 31, 2025	Sep. 30, 2024
Goodwill [Line Items]
Beginning balance		$ 2,015.7	$ 2,021.4
Acquisitions	[1]	(0.1)	0.1
Divestiture			(5.8)
Ending balance		2,015.6	2,015.7
Maintenance Services
Goodwill [Line Items]
Beginning balance		1,797.7	1,803.4
Acquisitions	[1]	(0.1)	0.1
Divestiture			(5.8)
Ending balance		1,797.6	1,797.7
Development Services
Goodwill [Line Items]
Beginning balance		218.0	218.0
Acquisitions	[1]	0.0	0.0
Divestiture			0.0
Ending balance		$ 218.0	$ 218.0

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