Investment Portfolio - Schedule of Balance Sheet Information for COPJV (Details) - USD ($) $ in Millions	Sep. 30, 2024		Jun. 30, 2024	Dec. 31, 2023		Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investments, at fair value	$ 13,943.4	[1],[2]		$ 14,649.3	[3],[4],[5],[6],[7]
Total assets	15,149.0			15,469.0
Total liabilities	8,478.0			8,620.0
Member's equity	6,671.0		$ 6,707.0	6,849.0		$ 6,970.0	$ 6,915.0	$ 7,012.0
Credit Opportunities Partners JV, LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investments, at fair value	3,462.4			3,470.8
Cash and other assets	405.0			272.2
Total assets	3,867.4			3,743.0
Debt	1,722.1			1,840.1
Other liabilities	563.9			306.5
Total liabilities	2,286.0			2,146.6
Member's equity	$ 1,581.4			$ 1,596.4

[1] Security may be an obligation of one or more entities affiliated with the named company

[2] See Note 8 for additional information regarding the fair value of the Company’s financial instruments

[3] Security is classified as Level 1 or 2 in the Company's fair value hierarchy (see Note 8).

[4] Security is non-income producing.

[5] Security or portion thereof is pledged as collateral supporting the amounts outstanding under the Senior Secured Revolving Credit Facility (see Note 9).

[6] Security may be an obligation of one or more entities affiliated with the named company.

[7] Fair value determined by the Company’s board of directors (see Note 8).