FAIR VALUE MEASUREMENTS - Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Purchases	$ 25.0	$ 193.1
Total realized / unrealized losses included in OCI	(96.4)	35.1	$ (22.1)
Net Unrealized Loss On Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized / unrealized losses included in OCI	(102.0)	(3.1)	0.0
Convertible debt investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized / unrealized gains included in net earnings	3.7	0.3
Fair value, inputs, level 3 \| Estimate of Fair Value Measurement \| Fair Value, Measurements, Recurring \| Convertible debt investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at beginning of year	190.3	0.0
Fair value at end of year	$ 117.0	$ 190.3	$ 0.0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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The aggregate amount of income from investments (for example, dividends) not considered a component of the entity's core operations.

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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