FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Measurements of Cash and Cash Equivalents, Restricted Cash, Investments, Derivatives, and Unfunded Revolving and Delayed Draw Loan Commitments (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	$ 29,499.3	$ 29,484.8	[1]
Unfunded revolving and delayed draw loan commitments	(33.0)	(32.0)
Derivatives	(62.0)	(155.0)
Foreign currency forward contract
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	11.0	(13.0)
Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	36.0	77.0
Total
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	29,482.0	29,468.0
Level 1
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	35.0	20.0
Unfunded revolving and delayed draw loan commitments	0.0	0.0
Level 1 | Foreign currency forward contract
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	0.0	0.0
Level 1 | Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	0.0	0.0
Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	609.0	756.0
Unfunded revolving and delayed draw loan commitments	0.0	0.0
Level 2 | Foreign currency forward contract
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	11.0	(13.0)
Level 2 | Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	36.0	77.0
Level 3
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	28,838.0	28,692.0
Unfunded revolving and delayed draw loan commitments	(33.0)	(32.0)
Level 3 | Foreign currency forward contract
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	0.0	0.0
Level 3 | Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	0.0	0.0
Investments measured at net asset value
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	$ 17.0	$ 17.0

[1] As of December 31, 2025, the estimated net unrealized gain for federal tax purposes was approximately $300 million based on a tax cost basis of $29.2 billion. As of December 31, 2025, the estimated aggregate gross unrealized gain for federal income tax purposes was approximately $1.3 billion and the estimated aggregate gross unrealized loss for federal income tax purposes was approximately $1.0 billion.