CONSOLIDATED INVESTMENT PRODUCTS - Fair Value Hierarchy Levels of Investments Held and Notes Issued by Consolidated Investment Products (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Segment Reporting, Other Significant Reconciling Items [Line Items]
Total assets at fair value	$ 8,611.3	$ 8,531.4
Consolidated
Segment Reporting, Other Significant Reconciling Items [Line Items]
Real estate investments	502.6	552.0
Total assets at fair value	8,611.3	8,531.4
Consolidated | Quoted Prices in Active Markets for Identical Assets (Level 1)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Real estate investments	0.0	0.0
Total assets at fair value	128.1	177.5
Consolidated | Significant Other Observable Inputs (Level 2)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Real estate investments	0.0	0.0
Total assets at fair value	7,084.9	6,979.7
Consolidated | Significant Unobservable Inputs (Level 3)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Real estate investments	0.0	0.0
Total assets at fair value	490.8	368.6
Consolidated | Investments Measured at NAV as a practical expedient
Segment Reporting, Other Significant Reconciling Items [Line Items]
Real estate investments	502.6	552.0
Total assets at fair value	907.5	1,005.6
Consolidated | Bank Loans
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	6,571.1	6,315.1
Consolidated | Bank Loans | Quoted Prices in Active Markets for Identical Assets (Level 1)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	0.0	0.0
Consolidated | Bank Loans | Significant Other Observable Inputs (Level 2)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	6,187.2	6,069.8
Consolidated | Bank Loans | Significant Unobservable Inputs (Level 3)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	383.9	245.3
Consolidated | Bank Loans | Investments Measured at NAV as a practical expedient
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	0.0	0.0
Consolidated | Bonds
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	727.3	697.5
Consolidated | Bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	14.0	8.8
Consolidated | Bonds | Significant Other Observable Inputs (Level 2)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	713.3	688.2
Consolidated | Bonds | Significant Unobservable Inputs (Level 3)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	0.0	0.5
Consolidated | Bonds | Investments Measured at NAV as a practical expedient
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	0.0	0.0
Consolidated | Equity securities, Equity and fixed income mutual funds
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	226.4	274.9
Equity and fixed income mutual funds, and investments in other private equity funds	171.4	230.7
Consolidated | Equity securities, Equity and fixed income mutual funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	88.3	129.9
Equity and fixed income mutual funds, and investments in other private equity funds	25.8	38.8
Consolidated | Equity securities, Equity and fixed income mutual funds | Significant Other Observable Inputs (Level 2)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	38.8	29.8
Equity and fixed income mutual funds, and investments in other private equity funds	145.6	191.9
Consolidated | Equity securities, Equity and fixed income mutual funds | Significant Unobservable Inputs (Level 3)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Bank loan, bonds and equity securities	99.3	115.2
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
Segment Reporting, Other Significant Reconciling Items [Line Items]
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
Consolidated | Investments in other private equity funds
Segment Reporting, Other Significant Reconciling Items [Line Items]
Equity and fixed income mutual funds, and investments in other private equity funds	412.5	461.2
Consolidated | Investments in other private equity funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Segment Reporting, Other Significant Reconciling Items [Line Items]
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)
Segment Reporting, Other Significant Reconciling Items [Line Items]
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)
Segment Reporting, Other Significant Reconciling Items [Line Items]
Equity and fixed income mutual funds, and investments in other private equity funds	7.6	7.6
Consolidated | Investments in other private equity funds | Investments Measured at NAV as a practical expedient
Segment Reporting, Other Significant Reconciling Items [Line Items]
Equity and fixed income mutual funds, and investments in other private equity funds	$ 404.9	$ 453.6