Investments - Summary of Investments (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Fixed income securities	$ 234.9	$ 419.0
Equity securities	877.3	1,090.0
Other	69.0	69.9
Total investments	1,181.2	1,578.9
Less short-term investments	(121.2)	(290.9)
Long-term investments	$ 1,060.0	$ 1,288.0

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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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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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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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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