Segment Information - Summarized Operating Results by Segment (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment information
Number of reportable segments | segment									1
ENI revenue	$ 162.9	$ 117.9	$ 133.3	$ 109.7	$ 120.8	$ 127.5	$ 122.6	$ 128.6	$ 523.8	$ 499.5	$ 594.6
ENI operating expenses									234.1	247.2	214.3
Earnings before variable compensation									289.7	252.3	380.3
Variable compensation									130.5	112.1	138.0
ENI operating earnings (after variable comp)									159.2	140.2	242.3
Affiliate key employee distributions									13.4	8.5	20.1
Operating income	48.5	28.7	36.1	32.5	26.9	34.2	29.9	40.7	145.8	131.7	222.2
Net interest expense									(24.6)	(27.9)	(30.0)
Net investment income									8.3	(0.3)	21.0
Gain on sale of subsidiaries									48.6	241.3
Net income attributable to non-controlling interests in consolidated Funds									(68.0)	(28.8)	(16.1)
Income tax (expense) benefit									(50.0)	(97.1)	(10.5)
Income from discontinued operations, net of tax	0.8	1.2	53.4	21.9	$ 15.7	$ 2.1	$ 26.7	$ 23.3	77.3	67.8	37.3
Gain on disposal of discontinued operations, net of tax	$ (3.6)	$ 185.4	$ 509.2	$ 0.0					691.0	0.0	0.0
Net income attributable to controlling interests									828.4	286.7	223.9
Operating Segments | Quant & Solutions
Segment information
ENI revenue									488.1	354.8	380.6
ENI operating expenses									160.8	149.0	160.6
Earnings before variable compensation									327.3	205.8	220.0
Variable compensation									100.8	72.8	75.6
ENI operating earnings (after variable comp)									226.5	133.0	144.4
Affiliate key employee distributions									12.4	4.3	6.4
Operating income									214.1	128.7	138.0
Net interest expense									0.0	0.0	0.0
Net investment income									0.0	0.0	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	0.0
Income tax (expense) benefit									0.0	0.0	0.0
Income from discontinued operations, net of tax									0.0	0.0	0.0
Gain on disposal of discontinued operations, net of tax									0.0
Net income attributable to controlling interests									214.1	128.7	138.0
Operating Segments | Liquid Alpha
Segment information
ENI revenue										111.1	180.3
ENI operating expenses										39.4	54.1
Earnings before variable compensation										71.7	126.2
Variable compensation										29.0	43.7
ENI operating earnings (after variable comp)										42.7	82.5
Affiliate key employee distributions										3.9	13.7
Operating income										38.8	68.8
Net interest expense										0.0	0.0
Net investment income										0.0	0.0
Gain on sale of subsidiaries										0.0
Net income attributable to non-controlling interests in consolidated Funds										0.0	0.0
Income tax (expense) benefit										0.0	0.0
Income from discontinued operations, net of tax										0.0	0.0
Net income attributable to controlling interests										38.8	68.8
Other
Segment information
ENI revenue									35.4	26.4	25.5
ENI operating expenses									32.0	45.1	57.4
Earnings before variable compensation									3.4	(18.7)	(31.9)
Variable compensation									28.8	6.1	12.0
ENI operating earnings (after variable comp)									(25.4)	(24.8)	(43.9)
Affiliate key employee distributions									1.0	0.3	0.0
Operating income									(26.4)	(25.1)	(43.9)
Net interest expense									(22.3)	(21.6)	(21.0)
Net investment income									0.0	0.0	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	0.0
Income tax (expense) benefit									(47.1)	(32.5)	(37.7)
Income from discontinued operations, net of tax									0.0	0.0	0.0
Gain on disposal of discontinued operations, net of tax									0.0
Net income attributable to controlling interests									(95.8)	(79.2)	(102.6)
Reconciling Adjustments
Segment information
ENI revenue									0.3	7.2	8.2
ENI operating expenses									41.3	13.7	(57.8)
Earnings before variable compensation									(41.0)	(6.5)	66.0
Variable compensation									0.9	4.2	6.7
ENI operating earnings (after variable comp)									(41.9)	(10.7)	59.3
Affiliate key employee distributions									0.0	0.0	0.0
Operating income									(41.9)	(10.7)	59.3
Net interest expense									(2.3)	(6.3)	(9.0)
Net investment income									8.3	(0.3)	21.0
Gain on sale of subsidiaries									48.6	241.3
Net income attributable to non-controlling interests in consolidated Funds									(68.0)	(28.8)	(16.1)
Income tax (expense) benefit									(2.9)	(64.6)	27.2
Income from discontinued operations, net of tax									77.3	67.8	37.3
Gain on disposal of discontinued operations, net of tax									691.0
Net income attributable to controlling interests									$ 710.1	$ 198.4	$ 119.7