Investments of Operating Entities and Consolidated Funds - Variable Interest Entities (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Total assets of nonconsolidated variable interest entities	$ 6,100.0	$ 5,100.0
Total liabilities of nonconsolidated variable interest entities	331.8	157.6
Variable Interest Entity, Nonconsolidated, Comparison of Carrying Amount of Assets and Liabilities to Maximum Loss Exposure	224.1	301.4
Maximum exposure regarding nonconsolidated variable interest entities	$ 256.2	$ 332.4