Consolidated Investment Products (CIP) - Narrative (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) entity	Jun. 30, 2020 USD ($) entity	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Variable Interest Entity [Line Items]
Number of entities no longer consolidated | entity		5	6
Number of deconsolidated voting right entities | entity		4	11
Pay interest at Libor or Euribor plus (percent)		12.00%
Collateral assets in default (percent)		0.61%
Weighted average maturity (years)		10 years 9 months 29 days
Notes issued by collateralized loan obligations terms of arrangements interest rate margin spread low		0.40%
Notes issued by collateralized loan obligations terms of arrangements interest rate margin spread high		8.51%
Investments of CIP		$ 8,304,800,000		$ 7,910,000,000.0
De-consolidated
Variable Interest Entity [Line Items]
Carrying value and maximum risk of loss with respect to VIEs in which the Company is not primary beneficiary		154,600,000		152,000,000.0
Gain (loss) on deconsolidation		0
Investments of CIP	$ 216,800,000	$ 284,400,000	$ 216,800,000
Consolidated
Variable Interest Entity [Line Items]
Number of consolidated VIEs | entity		6	4
Number of consolidated voting right entities | entity		3	0
Investments of CIP		$ 8,304,800,000		7,910,000,000.0
Bank loans
Variable Interest Entity [Line Items]
CLO Collateral Assets		7,043,200,000
Bank loans | Consolidated
Variable Interest Entity [Line Items]
CLO Collateral Assets		7,053,800,000		6,864,500,000
Senior Secured Bank Loans And Bonds
Variable Interest Entity [Line Items]
Fair value, option, aggregate differences, long-term debt instruments		84,200,000		208,600,000
Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Gains and losses included in the Condensed Consolidated Statements of Income	0		$ 10,800,000
Real Estate Investments, Net	$ 0		$ 0		$ 89,400,000	$ 78,600,000
Significant Unobservable Inputs (Level 3) | Consolidated
Variable Interest Entity [Line Items]
Investments of CIP		0		0
Significant Unobservable Inputs (Level 3) | Bank loans | Consolidated
Variable Interest Entity [Line Items]
CLO Collateral Assets		$ 0		$ 0