RESTRUCTURING AND RELATED CHARGES - Rollforward of Restructuring Accrual (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Restructuring Reserve [Roll Forward]
Accrual balance at beginning	$ 10.2	$ 33.6
Provisions	10.3	45.6
Cash expenditures	(10.1)	(64.8)
Non-cash items	0.2	0.0
Accrual balance at ending	10.2	10.2
Adoption of ASU 842
Restructuring Reserve [Roll Forward]
Accrual balance at beginning		(4.2)
Termination Benefits
Restructuring Reserve [Roll Forward]
Accrual balance at beginning	3.9	6.6
Provisions	5.7	4.0
Cash expenditures	(4.7)	(7.0)
Non-cash items	0.3	(0.3)
Accrual balance at ending	4.6	3.9
Termination Benefits | Adoption of ASU 842
Restructuring Reserve [Roll Forward]
Accrual balance at beginning		0.0
Other Costs
Restructuring Reserve [Roll Forward]
Accrual balance at beginning	6.3	27.0
Provisions	4.6	41.6
Cash expenditures	(5.4)	(57.8)
Non-cash items	(0.1)	0.3
Accrual balance at ending	$ 5.6	6.3
Other Costs | Adoption of ASU 842
Restructuring Reserve [Roll Forward]
Accrual balance at beginning		$ (4.2)