Investment Portfolio - Operations Information for COPJV (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investment income		$ 449.0	$ 411.0	$ 379.0	$ 396.0	$ 364.0	$ 360.0	$ 206.0	$ 151.0	$ 1,635.0	$ 1,081.0	$ 639.0
Interest expense	[1]									365.0	231.0	170.0
Professional services										15.0	12.0	7.0
Total operating expenses										811.0	515.0	298.0
Net investment income before taxes										884.0	596.0	$ 341.0
Credit Opportunities Partners JV, LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investment income										300.9	189.9
Interest expense										69.6	40.3
Custodian and accounting fees										1.3	1.1
Administrative services										10.3	6.7
Professional services										0.1	0.7
Other										0.3	0.5
Total operating expenses										81.6	49.3
Net investment income before taxes										219.3	140.6
Net realized and unrealized losses										(155.6)	56.3
Net increase in net assets resulting from operations										$ 63.7	$ 196.9

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