Investments - Summary of Investments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Investment Holdings [Line Items]
Total investments, at fair value	$ 554.3	$ 504.8
Investments in equity method investees	785.5	682.2
Other investments	94.1	83.5
Total	1,433.9	1,270.5
Sponsored funds and separate accounts
Investment Holdings [Line Items]
Investments, at fair value	332.6	303.4
Investments related to long-term incentive plans
Investment Holdings [Line Items]
Investments, at fair value	164.0	146.6
Other equity and debt investments
Investment Holdings [Line Items]
Investments, at fair value	$ 57.7	$ 54.8

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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