Investment Portfolio - Operations Information for COPJV (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses
Interest expense	[1]	$ 117.0	$ 96.0	$ 349.0	$ 256.0
Professional services		3.0	4.0	10.0	12.0
Net investment income		234.0	217.0	692.0	640.0
Credit Opportunities Partners JV, LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Total investment income		99.3	76.7	289.8	213.4
Operating expenses
Interest expense		30.4	19.9	91.6	44.8
Custodian and accounting fees		0.4	0.3	1.2	1.2
Administrative services		2.3	2.8	7.1	7.4
Professional services		0.2	0.0	0.4	0.2
Other		0.3	0.0	0.9	0.1
Total expenses		33.6	23.0	101.2	53.7
Net investment income		65.7	53.7	188.6	159.7
Net realized and unrealized gain (loss)		25.8	(49.4)	(25.3)	(112.8)
Net increase in net assets resulting from operations		$ 91.5	$ 4.3	$ 163.3	$ 46.9

[1] See Note 9 for a discussion of the Company’s financing arrangements.