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Concentration Risk - Schedule of Revenue Concentration by Asset Class (Details) - Product Concentration Risk
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Equity Assets      
Concentration Risk [Line Items]      
Concentration risk 40.00% 41.00% 38.00%
Money Market Assets      
Concentration Risk [Line Items]      
Concentration risk 40.00% 37.00% 41.00%
Fixed-Income Assets      
Concentration Risk [Line Items]      
Concentration risk 14.00% 16.00% 17.00%