Revenue - Schedule of Disaggregation of Revenue (Details) - Management fees - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Management fee revenue	$ 102.2	$ 103.8
Quant & Solutions | U.S.
Disaggregation of Revenue [Line Items]
Management fee revenue	77.0	74.4
Quant & Solutions | Non-U.S.
Disaggregation of Revenue [Line Items]
Management fee revenue	25.2	24.5
Other | U.S.
Disaggregation of Revenue [Line Items]
Management fee revenue	0.0	3.7
Other | Non-U.S.
Disaggregation of Revenue [Line Items]
Management fee revenue	$ 0.0	$ 1.2