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

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