FINANCIAL HIGHLIGHTS - Financial Highlights (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment Company, Financial Highlights [Roll Forward]
Net asset value, beginning of period (in dollars per share)	$ 19.24	$ 18.40	$ 18.96	$ 16.97	$ 17.32	$ 17.12	$ 16.65	$ 16.45	$ 16.46	$ 16.82
Issuances of common stock (in dollars per share)	0.12	0.01	0.10	0.11	0	0.02	0		0	0.01
Issuances of common stock (in dollars per share)								(0.01)
Conversion of 2024 Convertible Notes (in dollars per share)	0.01	0	0	0	0	0	0	0.04	0	0
Repurchases of common stock (in dollars per share)	0	0	0	0	0.11	0	0	0	0
Repurchases of common stock (in dollars per share)										(0.01)
Deemed contribution from Ares Capital Management (in dollars per share)						0	0	0.13	0	0
Net investment income for period (in dollars per share)	2.25	2.28	2.19	1.66	1.87	1.90	1.63	1.20	1.57	1.62
Net realized and unrealized gains (losses) for period (in dollars per share)	0.19	0.47	(0.98)	1.84	(0.73)	(0.04)	0.38	0.36	(0.06)	(0.41)
Net increase in stockholders' equity resulting from operations (in dollars per share)	2.57	2.76	1.31	3.61	1.25	1.88	2.01	1.72	1.51	1.21
Total distributions to stockholders (in dollars per share)	(1.92)	(1.92)	(1.87)	(1.62)	(1.60)	(1.68)	(1.54)	(1.52)	(1.52)	(1.57)
Net asset value, end of period (in dollars per share)	19.89	19.24	18.40	18.96	16.97	17.32	17.12	16.65	16.45	16.46
Per share market value at end of period (in dollars per share)	$ 21.89	$ 20.03	$ 18.47	$ 21.19	$ 16.89	$ 18.65	$ 15.58	$ 15.72	$ 16.49	$ 14.25	$ 15.61
Total return based on market value	19.80%	19.94%	(3.83%)	36.18%	(0.86%)	30.49%	8.91%	4.55%	26.39%	1.35%
Total return based on net asset value	13.83%	15.65%	7.13%	21.97%	5.20%	12.14%	12.10%	10.53%	9.15%	7.16%
Shares outstanding at end of period (in shares)	672	582	519	468	423	431	426	426	314	314
Ratio/Supplemental Data:
Net assets at end of period	$ 13,355	$ 11,201	$ 9,555	$ 8,868	$ 7,176	$ 7,467	$ 7,300	$ 7,098	$ 5,165	$ 5,173
Ratio of operating expenses to average net assets	12.26%	12.78%	10.19%	13.05%	10.27%	9.92%	8.63%	9.45%	9.59%	9.51%
Ratio of net investment income to average net assets	11.10%	12.10%	11.73%	9.19%	11.39%	11.01%	9.60%	7.65%	9.58%	9.75%
Portfolio turnover rate	39.00%	26.00%	37.00%	60.00%	40.00%	38.00%	54.00%	51.00%	39.00%	42.00%