PROPERTY, PLANT AND EQUIPMENT - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	May 30, 2025
Property, Plant and Equipment [Line Items]
Depreciation and depletion expense	$ 95.1	$ 97.9	$ 94.4
Net change to property, plant and equipment	4.0
Increase in property, plant and equipment from inventory transfer	6.9
Assets held-for-sale				$ 15.0
Loss on impairment of long-lived assets	53.7	193.4
Fortress long-lived assets, net
Property, Plant and Equipment [Line Items]
Loss on impairment of long-lived assets	$ 0.7
Lithium long-lived assets, net
Property, Plant and Equipment [Line Items]
Loss on impairment of long-lived assets		$ 74.8