Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 238.5	$ 207.1	$ 116.3
Other comprehensive income/(loss), net of tax:
Foreign currency translation adjustment	3.2	(11.7)	13.3
Cash flow hedges	35.1	(53.5)	0.0
Pension liabilities adjustment	0.5	(0.3)	1.5
Reclassification of adjustment for losses included in net income:
Periodic pension costs (included in compensation and benefits)	0.0	0.0	0.2
Reclassification adjustment for losses included in net income	0.0	0.0	0.2
Other comprehensive income/(loss)	38.8	(65.5)	15.0
Comprehensive income	$ 277.3	$ 141.6	$ 131.3