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	Dec. 31, 2025		Dec. 31, 2024
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	$ 29,484.8	[1]	$ 26,719.9	[2]
Unfunded revolving and delayed draw loan commitments	(32.0)		(29.0)
Derivatives	(155.0)		(62.0)
Foreign currency forward contract
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	(13.0)		24.0
Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	77.0		2.0
Total
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	29,468.0		26,711.0
Level 1
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	20.0		33.0
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	756.0		587.0
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	(13.0)		24.0
Level 2 | Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	77.0		2.0
Level 3
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	28,692.0		26,091.0
Unfunded revolving and delayed draw loan commitments	(32.0)		(29.0)
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		$ 9.0

[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.

[2] 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.