Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
ENI revenue	$ 96.3	$ 95.5	$ 188.1	$ 207.7
ENI operating expenses	52.0	25.6	99.6	64.8
Earnings Before Variable Compensation	44.3	69.9	88.5	142.9
Variable compensation	22.7	22.7	45.9	50.6
Operating Earnings After Variable Compensation	21.6	47.2	42.6	92.3
Affiliate key employee distributions	1.2	0.5	2.4	2.4
Earnings after Affiliate key employee distributions	20.4	46.7	40.2	89.9
Net interest expense	(3.9)	(4.7)	(7.7)	(11.2)
Investment income (loss)	0.2	(0.7)	0.5	(0.8)
Loss on extinguishment of debt	0.0	0.0	0.0	(3.2)
Net income attributable to non-controlling interests in consolidated Funds	(0.1)	0.0	(0.1)	0.0
Income tax expense	(5.5)	(12.7)	(10.6)	(22.3)
Net income attributable to controlling interests	11.4	28.6	23.4	52.4
Consolidated Funds
Segment Reporting Information [Line Items]
ENI revenue	1.3	0.0	2.0	0.0
Investment income (loss)	0.5		1.6
Operating Segments | Quant & Solutions
Segment Reporting Information [Line Items]
ENI revenue	95.0	95.5	186.1	207.7
ENI operating expenses	47.3	39.7	90.9	80.8
Earnings Before Variable Compensation	47.7	55.8	95.2	126.9
Variable compensation	22.0	21.7	44.5	48.0
Operating Earnings After Variable Compensation	25.7	34.1	50.7	78.9
Affiliate key employee distributions	1.2	0.5	2.4	2.4
Earnings after Affiliate key employee distributions	24.5	33.6	48.3	76.5
Net interest expense	0.0	0.0	0.0	0.0
Investment income (loss)		0.0		0.0
Loss on extinguishment of debt				0.0
Net income attributable to non-controlling interests in consolidated Funds	0.0		0.0
Income tax expense	0.0	0.0	0.0	0.0
Net income attributable to controlling interests	24.5	33.6	48.3	76.5
Operating Segments | Consolidated Funds | Quant & Solutions
Segment Reporting Information [Line Items]
Investment income (loss)	0.0		0.0
Other | Other
Segment Reporting Information [Line Items]
ENI revenue	0.0	0.0	0.0	0.0
ENI operating expenses	3.9	4.4	7.4	8.9
Earnings Before Variable Compensation	(3.9)	(4.4)	(7.4)	(8.9)
Variable compensation	0.7	1.0	1.4	2.6
Operating Earnings After Variable Compensation	(4.6)	(5.4)	(8.8)	(11.5)
Affiliate key employee distributions	0.0	0.0	0.0	0.0
Earnings after Affiliate key employee distributions	(4.6)	(5.4)	(8.8)	(11.5)
Net interest expense	(3.5)	(4.6)	(6.9)	(9.2)
Investment income (loss)		0.0		0.0
Loss on extinguishment of debt				0.0
Net income attributable to non-controlling interests in consolidated Funds	0.0		0.0
Income tax expense	(4.4)	(6.3)	(8.8)	(15.1)
Net income attributable to controlling interests	(12.5)	(16.3)	(24.5)	(35.8)
Other | Consolidated Funds | Other
Segment Reporting Information [Line Items]
Investment income (loss)	0.0		0.0
Reconciling Adjustments
Segment Reporting Information [Line Items]
ENI revenue	1.3	0.0	2.0	0.0
ENI operating expenses	0.8	(18.5)	1.3	(24.9)
Earnings Before Variable Compensation	0.5	18.5	0.7	24.9
Variable compensation	0.0	0.0	0.0	0.0
Operating Earnings After Variable Compensation	0.5	18.5	0.7	24.9
Affiliate key employee distributions	0.0	0.0	0.0	0.0
Earnings after Affiliate key employee distributions	0.5	18.5	0.7	24.9
Net interest expense	(0.4)	(0.1)	(0.8)	(2.0)
Investment income (loss)		(0.7)		(0.8)
Loss on extinguishment of debt				(3.2)
Net income attributable to non-controlling interests in consolidated Funds	(0.1)		(0.1)
Income tax expense	(1.1)	(6.4)	(1.8)	(7.2)
Net income attributable to controlling interests	(0.6)	$ 11.3	(0.4)	$ 11.7
Reconciling Adjustments | Consolidated Funds
Segment Reporting Information [Line Items]
Investment income (loss)	$ 0.5		$ 1.6