Investments - Summary of Investments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Fixed income securities	$ 0.7	$ 0.6
Equity securities	1,265.7	875.3
Other	80.2	78.2
Total investments	1,346.6	954.1
Less: Short-term investments	(0.7)	(0.6)
Long-term investments	$ 1,345.9	$ 953.5

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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Amount of investments classified as other.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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