Borrowings - Loans Payable of Consolidated Funds (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 6,523.3	$ 6,083.2
Fair Value	6,486.5	5,905.2
Fair value of liabilities	6,298.6	5,494.8
Revolving credit facilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	177.9	177.9
Fair Value	$ 177.9	$ 177.9
Weighted Average Interest Rate	6.46%	4.85%
Weighted Average Remaining Maturity in Years	5 years 18 days	4 years 3 months 18 days
Senior secured notes
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 6,171.9	$ 5,849.2
Fair Value	$ 6,097.9	$ 5,538.9
Weighted Average Interest Rate	6.32%	4.07%
Weighted Average Remaining Maturity in Years	8 years 11 months 26 days	9 years 7 months 6 days
Fair value of liabilities	$ 7.8	$ 235.6
Subordinated notes
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	173.5	56.1
Fair Value	$ 210.7	$ 188.4
Weighted Average Remaining Maturity in Years	9 years 1 month 28 days	9 years 8 months 8 days
Fair value of liabilities	$ 2.2