Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Management fee revenue	$ 807.0	$ 905.0	$ 858.0
Quant & Solutions | Global / non-U.S. equity
Disaggregation of Revenue [Line Items]
Management fee revenue	370.8	377.4	345.0
Alternatives | Alternatives
Disaggregation of Revenue [Line Items]
Management fee revenue	165.0	208.3	171.7
Liquid Alpha | Global / non-U.S. equity
Disaggregation of Revenue [Line Items]
Management fee revenue	90.7	112.9	120.6
Liquid Alpha | Fixed income
Disaggregation of Revenue [Line Items]
Management fee revenue	26.0	26.8	27.8
Liquid Alpha | U.S. equity
Disaggregation of Revenue [Line Items]
Management fee revenue	$ 154.5	$ 179.6	$ 192.9