Investments - Summary of Investments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Investment Holdings [Line Items]
Total investments, at fair value	$ 588.3	$ 504.8
Investments in equity method investees	814.3	716.2
Other investments	107.7	83.5
Total	1,510.3	1,304.5
Sponsored funds and separate accounts [Member]
Investment Holdings [Line Items]
Investments, at fair value	368.3	303.4
Investment related to long-term incentive plans [Member]
Investment Holdings [Line Items]
Investments, at fair value	160.0	146.6
Other equity and debt investments [Member]
Investment Holdings [Line Items]
Investments, at fair value	$ 60.0	$ 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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