Summary of Significant Accounting Policies - Principles of Consolidation (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	$ 21,250.4	$ 15,644.8	$ 13,808.8
Liabilities	15,544.2	$ 12,714.6
Collateralized Loan Obligations
Variable Interest Entity [Line Items]
Investment in CLOs	164.2
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	6,900.0
Liabilities	$ 6,600.0