Investment Portfolio - Schedule of Balance Sheet Information for COPJV (Details) - USD ($) $ in Millions	Jun. 30, 2024		Mar. 31, 2024	Dec. 31, 2023		Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investments, at fair value	$ 14,087.4	[1]		$ 14,649.3	[2],[3],[4],[5]
Total assets	15,101.0			15,469.0
Total liabilities	8,394.0			8,620.0
Member's equity	6,707.0		$ 6,812.0	6,849.0		$ 6,915.0	$ 6,983.0	$ 7,012.0
Credit Opportunities Partners JV, LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investments, at fair value	3,124.1			3,470.8
Cash and other assets	412.6			272.2
Total assets	3,536.7			3,743.0
Debt	1,629.4			1,840.1
Other liabilities	321.0			306.5
Total liabilities	1,950.4			2,146.6
Member's equity	$ 1,586.3			$ 1,596.4

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

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

[3] Security is non-income producing.

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

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