SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Accounting Policies [Abstract]
Interest paid	$ 173.5	$ 112.5	$ 61.6
Income taxes paid (refunded)	$ (18.2)	$ 27.2	$ 179.7