Summary of Significant Accounting Policies - Principles of Consolidation (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Variable Interest Entity [Line Items]
Consolidated VIEs, assets	$ 21,176.0	$ 21,403.0	$ 21,250.4
Consolidated VIEs, liabilities	15,391.5	14,581.7
Investment in CLOs	138.4
Investment fund	309.9
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Consolidated VIEs, assets	7,800.0	7,200.0
Consolidated VIEs, liabilities	$ 6,900.0	$ 6,200.0