CONSOLIDATED INVESTMENT PRODUCTS - Fair Value Hierarchy Levels of Investments Held and Notes Issued by Consolidated Investment Products (Details) - Consolidated - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Assets:
Real estate investments	$ 0.0	$ 438.6
Total assets at fair value	8,663.3	7,492.7
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	40.8	57.6
Significant Other Observable Inputs (Level 2)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	7,715.5	6,198.8
Significant Unobservable Inputs (Level 3)
Assets:
Real estate investments	0.0	0.0
Total assets at fair value	505.8	383.1
Investments Measured at NAV as a practical expedient
Assets:
Real estate investments	0.0	438.6
Total assets at fair value	401.2	853.2
Bank loans
Assets:
Bank loan, bonds and equity securities	7,345.5	5,793.0
Bank loans \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Bank loan, bonds and equity securities	0.0	0.0
Bank loans \| Significant Other Observable Inputs (Level 2)
Assets:
Bank loan, bonds and equity securities	6,958.7	5,494.5
Bank loans \| Significant Unobservable Inputs (Level 3)
Assets:
Bank loan, bonds and equity securities	386.8	298.5
Bank loans \| Investments Measured at NAV as a practical expedient
Assets:
Bank loan, bonds and equity securities	0.0	0.0
Bonds
Assets:
Bank loan, bonds and equity securities	770.7	605.5
Bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Bank loan, bonds and equity securities	22.6	17.2
Bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Bank loan, bonds and equity securities	743.6	588.3
Bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Bank loan, bonds and equity securities	4.5	0.0
Bonds \| Investments Measured at NAV as a practical expedient
Assets:
Bank loan, bonds and equity securities	0.0	0.0
Equity securities, Equity and fixed income mutual funds
Assets:
Bank loan, bonds and equity securities	125.8	144.5
Equity and fixed income mutual funds, and investments in other private equity funds	20.1	96.5
Equity securities, Equity and fixed income mutual funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Bank loan, bonds and equity securities	9.9	37.2
Equity and fixed income mutual funds, and investments in other private equity funds	8.3	3.2
Equity securities, Equity and fixed income mutual funds \| Significant Other Observable Inputs (Level 2)
Assets:
Bank loan, bonds and equity securities	1.4	22.7
Equity and fixed income mutual funds, and investments in other private equity funds	11.8	93.3
Equity securities, Equity and fixed income mutual funds \| Significant Unobservable Inputs (Level 3)
Assets:
Bank loan, bonds and equity securities	114.5	84.6
Equity and fixed income mutual funds, and investments in other private equity funds	0.0	0.0
Equity securities, Equity and fixed income mutual funds \| Investments Measured at NAV as a practical expedient
Assets:
Bank loan, bonds and equity securities	0.0	0.0
Equity and fixed income mutual funds, and investments in other private equity funds	0.0	0.0
Investments in other private equity funds
Assets:
Equity and fixed income mutual funds, and investments in other private equity funds	401.2	414.6
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
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
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
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	$ 401.2	$ 414.6