COMMITMENTS AND CONTINGENCIES - Schedule of Loan Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Other Commitments [Line Items]
Total net adjusted unfunded loan commitments	$ 32.0	$ 57.0
Revolving and delayed draw loan commitments
Other Commitments [Line Items]
Total commitments	2,766.3	2,915.8
Less: funded commitments	(482.1)	(526.2)
Less: unavailable delayed draw loan commitments due to borrowing base or other covenant restrictions	(12.9)	(13.0)
Total net adjusted unfunded loan commitments	2,284.2	2,389.6
Total net unfunded revolving and delayed draw loan commitments	2,271.3	2,376.6
Revolving loan commitments
Other Commitments [Line Items]
Total commitments	1,814.0	1,687.0
Less: funded commitments	(482.0)	(526.0)
Total net adjusted unfunded loan commitments	1,332.0	1,161.0
Delayed draw loan commitments
Other Commitments [Line Items]
Total commitments	952.0	1,229.0
Less: unavailable delayed draw loan commitments due to borrowing base or other covenant restrictions	(13.0)	(13.0)
Total net adjusted unfunded loan commitments	$ 939.0	$ 1,216.0