Investments of Operating Entities and Consolidated Funds - Variable Interest Entities (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Total assets of nonconsolidated variable interest entities	$ 3,200.0	$ 3,000.0
Total liabilities of nonconsolidated variable interest entities	415.6	499.2
Maximum exposure regarding nonconsolidated variable interest entities	$ 314.6	$ 260.9