Investments - Summary of Investments (Details) - USD ($) $ in Millions |
Mar. 31, 2024 |
Sep. 30, 2023 |
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| Investment Holdings [Line Items] | ||
| Total investments, at fair value | $ 899.7 | $ 872.8 |
| Investments in equity method investees | 1,216.7 | 1,089.2 |
| Other investments | 261.3 | 260.0 |
| Investments | 2,377.7 | 2,222.0 |
| Sponsored funds and separate accounts [Member] | ||
| Investment Holdings [Line Items] | ||
| Investments, at fair value | 588.6 | 630.5 |
| Investments related to long-term incentive plans [Member] | ||
| Investment Holdings [Line Items] | ||
| Investments, at fair value | 258.5 | 191.6 |
| Other equity and debt investments [Member] | ||
| Investment Holdings [Line Items] | ||
| Investments, at fair value | $ 52.6 | $ 50.7 |
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- Definition 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Sum of the carrying amounts as of the balance sheet date of all investments. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of investments classified as other. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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