Consolidated Investment Products - Schedule of Balances of Assets and Liabilities of CIPs Measured at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Assets [Abstract]
Investments, at fair value	$ 588.3	$ 504.8
CIPs [Member]
Assets [Abstract]
Investments, at fair value	5,820.1	4,074.0
Fair Value, Recurring [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	607.7	544.5
Fair Value, Recurring [Member] \| Level 1 [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	404.6	323.9
Fair Value, Recurring [Member] \| Level 2 [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	31.7	42.4
Fair Value, Recurring [Member] \| Level 3 [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	44.0	57.1
Fair Value, Recurring [Member] \| NAV as a Practical Expedient [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	127.4	121.1
Fair Value, Recurring [Member] \| CIPs [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	6,049.5	4,659.1
Fair Value, Recurring [Member] \| CIPs [Member] \| Level 1 [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	456.2	704.9
Fair Value, Recurring [Member] \| CIPs [Member] \| Level 2 [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	4,686.6	3,006.7
Fair Value, Recurring [Member] \| CIPs [Member] \| Level 3 [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	563.2	686.4
Fair Value, Recurring [Member] \| CIPs [Member] \| NAV as a Practical Expedient [Member]
Assets [Abstract]
Total Assets Measured at Fair Value	343.5	261.1
Equity and debt securities [Member] \| Fair Value, Recurring [Member] \| CIPs [Member]
Assets [Abstract]
Investments, at fair value	1,754.9	1,046.7
Equity and debt securities [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 1 [Member]
Assets [Abstract]
Investments, at fair value	310.8	177.6
Equity and debt securities [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 2 [Member]
Assets [Abstract]
Investments, at fair value	647.3	285.7
Equity and debt securities [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 3 [Member]
Assets [Abstract]
Investments, at fair value	453.3	322.3
Equity and debt securities [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| NAV as a Practical Expedient [Member]
Assets [Abstract]
Investments, at fair value	343.5	261.1
Loans [Member] \| Fair Value, Recurring [Member] \| CIPs [Member]
Assets [Abstract]
Investments, at fair value	3,975.8	2,688.1
Loans [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 1 [Member]
Assets [Abstract]
Investments, at fair value	0.0	0.0
Loans [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 2 [Member]
Assets [Abstract]
Investments, at fair value	3,955.3	2,663.2
Loans [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 3 [Member]
Assets [Abstract]
Investments, at fair value	20.5	24.9
Real estate [Member] \| Fair Value, Recurring [Member] \| CIPs [Member]
Assets [Abstract]
Investments, at fair value	89.4	339.2
Real estate [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 1 [Member]
Assets [Abstract]
Investments, at fair value	0.0	0.0
Real estate [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 2 [Member]
Assets [Abstract]
Investments, at fair value	0.0	0.0
Real estate [Member] \| Fair Value, Recurring [Member] \| CIPs [Member] \| Level 3 [Member]
Assets [Abstract]
Investments, at fair value	89.4	339.2
Collateralized Loan Obligations [Member]
Assets [Abstract]
Investments, at fair value	3,972.0	2,663.2
Collateralized Loan Obligations [Member] \| Fair Value, Recurring [Member]
Assets [Abstract]
Cash and cash equivalents of CLOs	145.4	527.3
Receivables of CLOs	84.0	57.8
Collateralized Loan Obligations [Member] \| Fair Value, Recurring [Member] \| Level 1 [Member]
Assets [Abstract]
Cash and cash equivalents of CLOs	145.4	527.3
Receivables of CLOs	0.0	0.0
Collateralized Loan Obligations [Member] \| Fair Value, Recurring [Member] \| Level 2 [Member]
Assets [Abstract]
Cash and cash equivalents of CLOs	0.0	0.0
Receivables of CLOs	84.0	57.8
Collateralized Loan Obligations [Member] \| Fair Value, Recurring [Member] \| Level 3 [Member]
Assets [Abstract]
Cash and cash equivalents of CLOs	0.0	0.0
Receivables of CLOs	$ 0.0	$ 0.0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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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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