Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
ENI revenue	$ 112.2	$ 109.7
ENI operating expenses	39.2	51.9
Earnings before variable compensation	73.0	57.8
Variable compensation	27.9	24.0
ENI operating earnings (after variable comp)	45.1	33.8
Affiliate key employee distributions	1.9	1.3
Earnings after Affiliate key employee distributions	43.2	32.5
Net interest expense	(6.5)	(6.2)
Net investment income	(0.1)	2.6
Loss on sale of subsidiary	0.0	(1.3)
Net loss attributable to non-controlling interests in consolidated Funds	0.0	(13.4)
Income tax expense	(9.6)	(9.1)
Loss on extinguishment of debt	(3.2)	0.0
Income from discontinued operations, net of tax		21.9
Net income attributable to controlling interests	23.8	27.0
Quant & Solutions
Segment Reporting Information [Line Items]
ENI revenue	112.2	103.5
ENI operating expenses	41.1	39.1
Earnings before variable compensation	71.1	64.4
Variable compensation	26.3	22.6
ENI operating earnings (after variable comp)	44.8	41.8
Affiliate key employee distributions	1.9	1.5
Earnings after Affiliate key employee distributions	42.9	40.3
Net interest expense	0.0	0.0
Net investment income	0.0	0.0
Loss on sale of subsidiary		0.0
Net loss attributable to non-controlling interests in consolidated Funds		0.0
Income tax expense	0.0	0.0
Loss on extinguishment of debt	0.0
Income from discontinued operations, net of tax		0.0
Net income attributable to controlling interests	42.9	40.3
Other
Segment Reporting Information [Line Items]
ENI revenue	0.0	6.3
ENI operating expenses	4.5	9.7
Earnings before variable compensation	(4.5)	(3.4)
Variable compensation	1.6	0.9
ENI operating earnings (after variable comp)	(6.1)	(4.3)
Affiliate key employee distributions	0.0	(0.2)
Earnings after Affiliate key employee distributions	(6.1)	(4.1)
Net interest expense	(4.6)	(5.4)
Net investment income	0.0	0.0
Loss on sale of subsidiary		0.0
Net loss attributable to non-controlling interests in consolidated Funds		0.0
Income tax expense	(8.8)	(8.3)
Loss on extinguishment of debt	0.0
Income from discontinued operations, net of tax		0.0
Net income attributable to controlling interests	(19.5)	(17.8)
Reconciling Adjustments
Segment Reporting Information [Line Items]
ENI revenue	0.0	(0.1)
ENI operating expenses	(6.4)	3.1
Earnings before variable compensation	6.4	(3.2)
Variable compensation	0.0	0.5
ENI operating earnings (after variable comp)	6.4	(3.7)
Affiliate key employee distributions	0.0	0.0
Earnings after Affiliate key employee distributions	6.4	(3.7)
Net interest expense	(1.9)	(0.8)
Net investment income	(0.1)	2.6
Loss on sale of subsidiary		(1.3)
Net loss attributable to non-controlling interests in consolidated Funds		(13.4)
Income tax expense	(0.8)	(0.8)
Loss on extinguishment of debt	(3.2)
Income from discontinued operations, net of tax		21.9
Net income attributable to controlling interests	$ 0.4	$ 4.5