COMMITMENTS AND CONTINGENCIES - Loan Commitments (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Other Commitments [Line Items]
Total unfunded equity commitments	$ 25.0	$ 32.0
Revolving and delayed draw loan commitments
Other Commitments [Line Items]
Total commitments	4,037.2	2,766.3
Less: funded commitments	(472.7)	(482.1)
Less: unavailable delayed draw loan commitments due to borrowing base or other covenant restrictions	(24.2)	(12.9)
Total unfunded equity commitments	3,564.5	2,284.2
Total net unfunded revolving and delayed draw loan commitments	3,540.3	2,271.3
Revolving loan commitments
Other Commitments [Line Items]
Total commitments	2,025.0	1,814.0
Less: funded commitments	(473.0)	(482.0)
Less: unavailable delayed draw loan commitments due to borrowing base or other covenant restrictions	(8.0)	0.0
Total unfunded equity commitments	1,544.0	1,332.0
Delayed draw loan commitments
Other Commitments [Line Items]
Total commitments	2,012.0	952.0
Less: unavailable delayed draw loan commitments due to borrowing base or other covenant restrictions	(16.0)	(13.0)
Total unfunded equity commitments	$ 1,996.0	$ 939.0