Segment Information - Summarized Operating Results by Segment (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2022 USD ($) segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Segment information
Number of reportable segments | segment									1
ENI revenue	$ 122.7	$ 86.8	$ 95.5	$ 112.2	$ 162.9	$ 117.9	$ 133.3	$ 109.7	$ 417.2	$ 523.8	$ 499.5
ENI operating expenses									143.9	234.1	247.2
Earnings before variable compensation									273.3	289.7	252.3
Variable compensation									100.3	130.5	112.1
ENI operating earnings (after variable comp)									173.0	159.2	140.2
Affiliate key employee distributions									5.1	13.4	8.5
Operating income	$ 47.9	$ 30.1	$ 46.7	$ 43.2	48.5	28.7	36.1	32.5	167.9	145.8	131.7
Net interest expense									(19.7)	(24.6)	(27.9)
Net investment loss									(0.2)	8.3	(0.3)
Loss on extinguishment of debt									(3.2)
Gain on sale of subsidiaries										48.6
Net income attributable to non-controlling interests in consolidated Funds										(68.0)	(28.8)
Income tax expense									(44.2)	(50.0)	(97.1)
Income from discontinued operations, net of tax					0.8	1.2	53.4	21.9	0.0	77.3	67.8
Gain on disposal of discontinued operations, net of tax					$ (3.6)	$ 185.4	$ 509.2	$ 0.0	0.0	691.0	0.0
Net income attributable to controlling interests									100.6	828.4	286.7
Operating Segments | Quant & Solutions
Segment information
ENI revenue									416.8	488.1	354.8
ENI operating expenses									165.5	160.8	149.0
Earnings before variable compensation									251.3	327.3	205.8
Variable compensation									96.0	100.8	72.8
ENI operating earnings (after variable comp)									155.3	226.5	133.0
Affiliate key employee distributions									5.1	12.4	4.3
Operating income									150.2	214.1	128.7
Net interest expense									0.0	0.0	0.0
Net investment loss									0.0	0.0	0.0
Loss on extinguishment of debt									0.0
Gain on sale of subsidiaries										0.0	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
Income from discontinued operations, net of tax										0.0	0.0
Gain on disposal of discontinued operations, net of tax										0.0
Net income attributable to controlling interests									150.2	214.1	128.7
Operating Segments | Liquid Alpha
Segment information
ENI revenue											111.1
ENI operating expenses											39.4
Earnings before variable compensation											71.7
Variable compensation											29.0
ENI operating earnings (after variable comp)											42.7
Affiliate key employee distributions											3.9
Operating income											38.8
Net interest expense											0.0
Net investment loss											0.0
Gain on sale of subsidiaries											0.0
Net income attributable to non-controlling interests in consolidated Funds											0.0
Income tax expense											0.0
Income from discontinued operations, net of tax											0.0
Net income attributable to controlling interests											38.8
Other
Segment information
ENI revenue									0.0	35.4	26.4
ENI operating expenses									16.6	32.0	45.1
Earnings before variable compensation									(16.6)	3.4	(18.7)
Variable compensation									4.3	28.8	6.1
ENI operating earnings (after variable comp)									(20.9)	(25.4)	(24.8)
Affiliate key employee distributions									0.0	1.0	0.3
Operating income									(20.9)	(26.4)	(25.1)
Net interest expense									(17.3)	(22.3)	(21.6)
Net investment loss									0.0	0.0	0.0
Loss on extinguishment of debt									0.0
Gain on sale of subsidiaries										0.0	0.0
Net income attributable to non-controlling interests in consolidated Funds										0.0	0.0
Income tax expense									(30.4)	(47.1)	(32.5)
Income from discontinued operations, net of tax										0.0	0.0
Gain on disposal of discontinued operations, net of tax										0.0
Net income attributable to controlling interests									(68.6)	(95.8)	(79.2)
Reconciling Adjustments
Segment information
ENI revenue									0.4	0.3	7.2
ENI operating expenses									(38.2)	41.3	13.7
Earnings before variable compensation									38.6	(41.0)	(6.5)
Variable compensation									0.0	0.9	4.2
ENI operating earnings (after variable comp)									38.6	(41.9)	(10.7)
Affiliate key employee distributions									0.0	0.0	0.0
Operating income									38.6	(41.9)	(10.7)
Net interest expense									(2.4)	(2.3)	(6.3)
Net investment loss									(0.2)	8.3	(0.3)
Loss on extinguishment of debt									(3.2)
Gain on sale of subsidiaries										48.6	241.3
Net income attributable to non-controlling interests in consolidated Funds										(68.0)	(28.8)
Income tax expense									(13.8)	(2.9)	(64.6)
Income from discontinued operations, net of tax										77.3	67.8
Gain on disposal of discontinued operations, net of tax										691.0
Net income attributable to controlling interests									$ 19.0	$ 710.1	$ 198.4