Investments - Schedule of Investments as a Percentage of Investments of Consolidated Funds (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Investments of Consolidated Funds	$ 5,007.3	$ 5,286.6
Percentage of investments in Consolidated Funds	100.00%	100.00%
Assets of the CLOs - Equity
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 0.5	$ 0.0
Percentage of assets of the CLOs	0.01%	0.00%
United States
Schedule of Investments [Line Items]
Investments of Consolidated Funds	$ 1,566.5	$ 1,696.6
Percentage of investments in Consolidated Funds	31.29%	32.09%
United States | Equity securities
Schedule of Investments [Line Items]
Equity securities	$ 17.8	$ 0.0
Percentage of equity securities	0.36%	0.00%
United States | Equity securities | Renewable Energy
Schedule of Investments [Line Items]
Equity securities	$ 17.8	$ 0.0
Percentage of equity securities	0.36%	0.00%
United States | Assets of the CLOs - Bonds
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 37.0	$ 75.3
Percentage of assets of the CLOs	0.74%	1.42%
United States | Assets of the CLOs - Equity
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 1.1	$ 0.0
Percentage of assets of the CLOs	0.02%	0.00%
United States | Assets of the CLOs - Loans
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 1,510.6	$ 1,621.3
Percentage of assets of the CLOs	30.17%	30.67%
United States | Total assets of the CLOs
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 1,548.7	$ 1,696.6
Percentage of assets of the CLOs	30.93%	32.09%
Europe
Schedule of Investments [Line Items]
Investments of Consolidated Funds	$ 3,204.9	$ 3,414.4
Percentage of investments in Consolidated Funds	64.00%	64.58%
Europe | Assets of the CLOs - Bonds
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 532.5	$ 610.3
Percentage of assets of the CLOs	10.63%	11.54%
Europe | Assets of the CLOs - Loans
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 2,671.9	$ 2,804.1
Percentage of assets of the CLOs	53.36%	53.04%
Europe | Total assets of the CLOs
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 3,204.9	$ 3,414.4
Percentage of assets of the CLOs	64.00%	64.58%
Global
Schedule of Investments [Line Items]
Investments of Consolidated Funds	$ 235.9	$ 175.6
Percentage of investments in Consolidated Funds	4.71%	3.33%
Global | Assets of the CLOs - Bonds
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 4.5	$ 4.5
Percentage of assets of the CLOs	0.09%	0.09%
Global | Assets of the CLOs - Loans
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 231.4	$ 171.1
Percentage of assets of the CLOs	4.62%	3.24%
Global | Total assets of the CLOs
Schedule of Investments [Line Items]
Total assets of the CLOs	$ 235.9	$ 175.6
Percentage of assets of the CLOs	4.71%	3.33%