Investment Portfolio - Operations Information for COPJV (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investment Company, Nonconsolidated Subsidiary [Line Items]
Interest expense	[1]	$ 96.0	$ 70.0	$ 256.0	$ 158.0
Professional services		4.0	5.0	12.0	9.0
Net investment income		217.0	201.0	640.0	395.0
Credit Opportunities Partners JV, LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Total investment income		76.7	56.6	213.4	128.8
Interest expense		19.9	12.7	44.8	27.0
Custodian and accounting fees		0.3	0.5	1.2	0.7
Administrative services expenses		2.8	2.7	7.4	4.5
Professional services		0.0	0.2	0.2	0.5
Other general and administrative expenses		0.0	0.2	0.1	0.3
Total expenses		23.0	16.3	53.7	33.0
Net investment income		53.7	40.3	159.7	95.8
Net increase (decrease) in net assets resulting from operations		(49.4)	(10.1)	(112.8)	56.6
Net increase in net assets resulting from operations		$ 4.3	$ 30.2	$ 46.9	$ 152.4

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