Borrowings - Outstanding Loans Payable of Consolidated Funds (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 1,950.7	$ 1,981.1
Loans Payable of Consolidated Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	5,473.9	5,606.4
Fair Value	5,440.7	5,563.0
Senior secured notes
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	5,257.0	5,442.2
Fair Value	$ 5,241.4	$ 5,358.9
Weighted Average Interest Rate	1.75%	1.74%
Weighted Average Remaining Maturity in Years	10 years 1 month 17 days	10 years 4 months 9 days
Subordinated notes, preferred shares and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 216.9	$ 164.2
Fair Value	$ 199.3	$ 204.1
Weighted Average Remaining Maturity in Years	10 years 3 months	10 years 5 months 26 days