STOCKHOLDERS' EQUITY AND EQUITY INSTRUMENTS - Schedule of Components and Changes in Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 316.6	$ 521.0	$ 265.2
Other comprehensive (loss) income before reclassifications	(13.8)	2.7
Amounts reclassified from AOCL	2.3	5.6
Net current period other comprehensive income (loss)	(11.5)	8.3
Ending balance	234.1	316.6	521.0
Foreign exchange gains (losses)	2.0	(0.2)	(1.6)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(96.4)	(104.7)	(115.3)
Ending balance	(107.9)	(96.4)	(104.7)
(Losses) and Gains on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1.3)	(1.4)
Other comprehensive (loss) income before reclassifications	(2.0)	(4.6)
Amounts reclassified from AOCL	2.5	4.7
Net current period other comprehensive income (loss)	0.5	0.1
Ending balance	(0.8)	(1.3)	(1.4)
Defined Benefit Pension | Defined Benefit Pension
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(6.2)	(6.6)
Other comprehensive (loss) income before reclassifications	(1.0)	(0.6)
Amounts reclassified from AOCL	0.9	1.0
Net current period other comprehensive income (loss)	(0.1)	0.4
Ending balance	(6.3)	(6.2)	(6.6)
Defined Benefit Pension | Other Post-Employment Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	1.4	1.7
Other comprehensive (loss) income before reclassifications	1.5	(0.2)
Amounts reclassified from AOCL	(1.1)	(0.1)
Net current period other comprehensive income (loss)	0.4	(0.3)
Ending balance	1.8	1.4	1.7
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(90.3)	(98.4)
Other comprehensive (loss) income before reclassifications	(12.3)	8.1
Amounts reclassified from AOCL	0.0	0.0
Net current period other comprehensive income (loss)	(12.3)	8.1
Ending balance	$ (102.6)	$ (90.3)	$ (98.4)