Investments - Gains and Losses on Investments within Change in Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Net (loss) gain on equity securities (level 1)	$ (136.4)	$ 392.3	$ 153.9
Net gain on equity securities (other)	15.1	5.1	0.0
Equity method loss on Other investments	(15.6)	0.0	0.0
Change in fair value of investments	(136.9)	397.4	153.9
Total net unrealized (loss) gain on equity securities	$ (165.9)	$ 397.4	$ 153.9

Equity Securities Without Readily Determinable Fair Value, Gain (Loss)

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

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

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Amount of realized and unrealized gain (loss) on investment.

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Amount of income (loss) for proportionate share of equity method investee's income (loss).

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