CONSOLIDATED INVESTMENT PRODUCTS - Fair Value Hierarchy Levels of Investments Held and Notes Issued by Consolidated Investment Products (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Bonds
Assets:
Bonds	$ 652.7	$ 674.2
Bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Bonds	5.6	11.8
Bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Bonds	647.1	640.5
Bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Bonds	0.0	21.9
Bonds \| Investments Measured at NAV as a Practical Expedient
Assets:
Bonds	0.0	0.0
Equity securities, Equity and fixed income mutual funds
Assets:
Equity securities	198.5	172.1
Equity securities, Equity and fixed income mutual funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Equity securities	75.7	50.8
Equity securities, Equity and fixed income mutual funds \| Significant Other Observable Inputs (Level 2)
Assets:
Equity securities	2.8	1.3
Equity securities, Equity and fixed income mutual funds \| Significant Unobservable Inputs (Level 3)
Assets:
Equity securities	120.0	120.0
Equity securities, Equity and fixed income mutual funds \| Investments Measured at NAV as a Practical Expedient
Assets:
Equity securities	0.0	0.0
Consolidated
Assets:
Real estate investments	4.0	4.1
Total assets at fair value	9,415.0	8,941.4
Consolidated \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	87.9	68.0
Consolidated \| Significant Other Observable Inputs (Level 2)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	8,505.2	7,963.9
Consolidated \| Significant Unobservable Inputs (Level 3)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	428.1	467.4
Consolidated \| Investments Measured at NAV as a Practical Expedient
Assets:
Real estate investments	4.0	4.1
Total assets at fair value	393.8	442.1
Consolidated \| Bank loans
Assets:
Bank loans	8,150.5	7,635.2
Consolidated \| Bank loans \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Bank loans	0.0	0.0
Consolidated \| Bank loans \| Significant Other Observable Inputs (Level 2)
Assets:
Bank loans	7,842.4	7,309.7
Consolidated \| Bank loans \| Significant Unobservable Inputs (Level 3)
Assets:
Bank loans	308.1	325.5
Consolidated \| Bank loans \| Investments Measured at NAV as a Practical Expedient
Assets:
Bank loans	0.0	0.0
Consolidated \| Equity securities, Equity and fixed income mutual funds
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	19.5	17.8
Consolidated \| Equity securities, Equity and fixed income mutual funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	6.6	5.4
Consolidated \| Equity securities, Equity and fixed income mutual funds \| Significant Other Observable Inputs (Level 2)
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	12.9	12.4
Consolidated \| Equity securities, Equity and fixed income mutual funds \| Significant Unobservable Inputs (Level 3)
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	0.0	0.0
Consolidated \| Equity securities, Equity and fixed income mutual funds \| Investments Measured at NAV as a Practical Expedient
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	0.0	0.0
Consolidated \| Investments in other private equity funds
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	389.8	438.0
Consolidated \| Investments in other private equity funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	0.0	0.0
Consolidated \| Investments in other private equity funds \| Significant Other Observable Inputs (Level 2)
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	0.0	0.0
Consolidated \| Investments in other private equity funds \| Significant Unobservable Inputs (Level 3)
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	0.0	0.0
Consolidated \| Investments in other private equity funds \| Investments Measured at NAV as a Practical Expedient
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	$ 389.8	$ 438.0