Investments - Schedule of Equity Method Investments (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Equity method investments	$ 1,078.6	$ 950.9
Operating Segments | Corporate Private Equity
Schedule of Investments [Line Items]
Equity method investments	324.3	282.4
Operating Segments | Real Assets
Schedule of Investments [Line Items]
Equity method investments	703.6	622.8
Operating Segments | Global Market Strategies
Schedule of Investments [Line Items]
Equity method investments	17.0	20.1
Operating Segments | Investment Solutions
Schedule of Investments [Line Items]
Equity method investments	$ 33.7	$ 25.6