INCOME AND EXCISE TAXES - Narrative (Details) - USD ($) $ 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
Investments, Owned, Federal Income Tax Note [Line Items]
Capital loss carryforward	$ 242.0
Capital loss carryforwards subject to limitations	92.0
Carry forward of excess distributable earnings	922.0		$ 631.0		$ 646.0
Excise tax expense	35.0		23.0		30.0
Refund request for overpayment of excise taxes	1.0		2.0
Tax cost basis	26,500.0		22,500.0
Aggregate gross unrealized gain for federal tax purposes	1,700.0		1,300.0
Unrealized losses	1,500.0		1,700.0
Amortized cost of investments	26,374.0	[1]	22,667.6	[2]
Tax reclassification of stockholders' equity, increase (decreased)	0.0		0.0		0.0
Total stockholders’ equity	13,355.0		11,201.0		9,555.0	$ 8,868.0	$ 7,176.0	$ 7,467.0	$ 7,300.0	$ 7,098.0	$ 5,165.0	$ 5,173.0
Income tax expense, including excise tax	73.0		20.0		55.0
Subsidiaries
Investments, Owned, Federal Income Tax Note [Line Items]
Income tax expense, including excise tax	38.0		(3.0)		25.0
Capital in Excess of Par Value
Investments, Owned, Federal Income Tax Note [Line Items]
Tax reclassification of stockholders' equity, increase (decreased)	(87.0)		(20.0)		(22.0)
Total stockholders’ equity	12,502.0		10,738.0		9,556.0	8,553.0
Accumulated Undistributed (Overdistributed) Earnings
Investments, Owned, Federal Income Tax Note [Line Items]
Tax reclassification of stockholders' equity, increase (decreased)	87.0		20.0		22.0
Total stockholders’ equity	852.0		462.0		$ (2.0)	$ 315.0
Retained Earnings, Accumulated Undistributed Net Investment Income
Investments, Owned, Federal Income Tax Note [Line Items]
Total stockholders’ equity	921.0		659.0
Retained Earnings, Accumulated Net Realized Losses
Investments, Owned, Federal Income Tax Note [Line Items]
Total stockholders’ equity	(316.0)		(256.0)
Retained Earnings, Accumulated Net Unrealized Gains
Investments, Owned, Federal Income Tax Note [Line Items]
Total stockholders’ equity	$ 247.0		$ 59.0

[1] As of December 31, 2024, the estimated net unrealized gain for federal tax purposes was $0.2 billion based on a tax cost basis of $26.5 billion. As of December 31, 2024, the estimated aggregate gross unrealized gain for federal income tax purposes was $1.7 billion and the estimated aggregate gross unrealized loss for federal income tax purposes was $1.5 billion.     

[2] As of December 31, 2023, the estimated net unrealized loss for federal tax purposes was $0.4 billion based on a tax cost basis of $22.5 billion. As of December 31, 2023, the estimated aggregate gross unrealized loss for federal income tax purposes was $1.7 billion and the estimated aggregate gross unrealized gain for federal income tax purposes was $1.3 billion.