Consolidated Investment Products (CIP) - Beginning And Ending Fair Value Measurements For Level 3 Assets And Liabilities (Details) - Significant Unobservable Inputs (Level 3) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance (Asset)	$ 89,400,000	$ 12,200,000	$ 78,600,000	$ 11,800,000
Purchases (Asset)	0		0
Sales (Asset)	0		0
Issuances (Asset)	0		0
Settlements (Asset)	0		0
Deconsolidation of CIP (Asset)	(89,400,000)		(89,400,000)
Gains and losses included in the Condensed Consolidated Statements of Income (Asset)	0	2,300,000	10,800,000	2,700,000
Ending balance (Asset)	$ 0	$ 14,500,000	$ 0	$ 14,500,000