CONSOLIDATED INVESTMENT PRODUCTS - Fair Value Hierarchy Levels of Investments Held And Notes Issued by Consolidated Investment Products (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Variable Interest Entity [Line Items]
Real estate investments	$ 463.6	$ 552.0
Investments of CIP	$ 8,765.9	$ 8,531.4
LIBOR spread on bank loan investments (percent)	13.38%
Pre-defined spreads on variable rate notes - minimum (percent)	0.40%
Pre-defined spreads on variable rate notes - maximum (percent)	8.68%
Percentage of collateral in default (percent)	0.07%	0.49%
Quoted Prices in Active Markets for Identical Assets (Level 1)
Variable Interest Entity [Line Items]
Real estate investments	$ 0.0	$ 0.0
Investments of CIP	106.5	177.5
Significant Other Observable Inputs (Level 2)
Variable Interest Entity [Line Items]
Real estate investments	0.0	0.0
Investments of CIP	6,944.5	6,979.7
Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Real estate investments	0.0	0.0
Investments of CIP	825.8	368.6
Bank loans
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	$ 6,837.2	6,315.1
Debt instrument, term	8 years
Bank loans | Quoted Prices in Active Markets for Identical Assets (Level 1)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	$ 0.0	0.0
Bank loans | Significant Other Observable Inputs (Level 2)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	6,140.1	6,069.8
Bank loans | Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	697.1	245.3
Bonds
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	669.8	697.5
Bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	13.3	8.8
Bonds | Significant Other Observable Inputs (Level 2)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	656.2	688.2
Bonds | Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	0.3	0.5
Equity securities
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	231.9	274.9
Equity securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	85.2	129.9
Equity securities | Significant Other Observable Inputs (Level 2)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	18.3	29.8
Equity securities | Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	128.4	115.2
Equity and fixed income mutual funds
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	137.9	230.7
Equity and fixed income mutual funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	8.0	38.8
Equity and fixed income mutual funds | Significant Other Observable Inputs (Level 2)
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	129.9	191.9
Equity and fixed income mutual funds | Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	0.0	0.0
Investments in other private equity funds
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	425.5	461.2
Investments in other private equity funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	0.0	0.0
Investments in other private equity funds | Significant Other Observable Inputs (Level 2)
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	0.0	0.0
Investments in other private equity funds | Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	0.0	7.6
Senior secured bank loans and bonds
Variable Interest Entity [Line Items]
Excess of unpaid principal balances over fair value of senior secured bank loans and bonds	340.9	544.1
Investments measured at NAV as a practical expedient
Variable Interest Entity [Line Items]
Real estate investments	463.6	552.0
Investments of CIP	889.1	1,005.6
Investments measured at NAV as a practical expedient | Bank loans
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	0.0	0.0
Investments measured at NAV as a practical expedient | Bonds
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	0.0	0.0
Investments measured at NAV as a practical expedient | Equity securities
Variable Interest Entity [Line Items]
Bank loans, bonds and equity securities	0.0	0.0
Investments measured at NAV as a practical expedient | Equity and fixed income mutual funds
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	0.0	0.0
Investments measured at NAV as a practical expedient | Investments in other private equity funds
Variable Interest Entity [Line Items]
Equity and fixed income mutual funds and other private equity funds	$ 425.5	$ 453.6