Investments of Operating Entities and Consolidated Funds - Operating Entities - Variable Interest Entities (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total assets of nonconsolidated variable interest entities	$ 7,100.0	$ 6,100.0
Total liabilities of nonconsolidated variable interest entities	1,100.0	617.5
Variable Interest Entity, Nonconsolidated, Comparison of Carrying Amount of Assets and Liabilities to Maximum Loss Exposure	127.6	241.2
Maximum exposure regarding nonconsolidated variable interest entities	$ 244.5	$ 261.7