Investments of Operating Entities and Consolidated Funds - Variable Interest Entities (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Total assets of nonconsolidated variable interest entities	$ 5,200.0	$ 5,300.0
Total liabilities of nonconsolidated variable interest entities	445.6	997.3
Maximum exposure regarding nonconsolidated variable interest entities	$ 471.3	$ 508.1