INCOME AND EXCISE TAXES - Dividends Paid Per Common Share (Details) - $ / shares	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
Investments, Owned, Federal Income Tax Note [Line Items]
Ordinary income (in dollars per share)	$ 1.92	$ 1.92	$ 1.80
Capital gains (in dollars per share)	0	0	0.07
Total (in dollars per share)	1.92	1.92	1.87	$ 1.62	$ 1.60	$ 1.68	$ 1.54	$ 1.52	$ 1.52	$ 1.57
Dividend income per share (in dollars per share)	$ 0.3137	$ 0.0296	$ 0.0582
Dividend Concentration Risk | Dividends | 2024 Interest-Related Dividends
Investments, Owned, Federal Income Tax Note [Line Items]
Composition, percent of fair value	88.60%
Dividend Concentration Risk | Dividends | 2023 Interest-Related Dividends
Investments, Owned, Federal Income Tax Note [Line Items]
Composition, percent of fair value		80.50%
Dividend Concentration Risk | Dividends | 2022 Interest-Related Dividends
Investments, Owned, Federal Income Tax Note [Line Items]
Composition, percent of fair value			76.60%