CONSOLIDATED INVESTMENT PRODUCTS - Fair Value Hierarchy Levels of Investments Held and Notes Issued by Consolidated Investment Products (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Bonds
Assets:
Bonds	$ 632.5	$ 674.2
Bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Bonds	5.9	11.8
Bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Bonds	626.6	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	136.6	172.1
Equity securities, Equity and fixed income mutual funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Equity securities	8.6	50.8
Equity securities, Equity and fixed income mutual funds \| Significant Other Observable Inputs (Level 2)
Assets:
Equity securities	6.0	1.3
Equity securities, Equity and fixed income mutual funds \| Significant Unobservable Inputs (Level 3)
Assets:
Equity securities	122.0	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	69.7	4.1
Total assets at fair value	9,527.1	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	20.7	68.0
Consolidated \| Significant Other Observable Inputs (Level 2)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	8,593.1	7,963.9
Consolidated \| Significant Unobservable Inputs (Level 3)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	461.6	467.4
Consolidated \| Investments Measured at NAV as a Practical Expedient
Assets:
Real estate investments	69.7	4.1
Total assets at fair value	451.7	442.1
Consolidated \| Bank loans
Assets:
Bank loans	8,291.6	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	7,952.0	7,309.7
Consolidated \| Bank loans \| Significant Unobservable Inputs (Level 3)
Assets:
Bank loans	339.6	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	14.7	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	6.2	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	8.5	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	382.0	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	$ 382.0	$ 438.0