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, 2024		Dec. 31, 2023
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Cash and cash equivalents	$ 635.0		$ 535.0
Restricted cash	225.0		29.0
Total investments	26,719.9	[1]	22,873.7	[2]
Unfunded revolving and delayed draw loan commitments	(29.0)		(32.0)
Foreign currency forward contract
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	24.0		(24.0)
Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	2.0		15.0
Total
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total investments	26,711.0		22,868.0
Level 1
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Cash and cash equivalents	635.0		535.0
Restricted cash	225.0		29.0
Total investments	33.0		48.0
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]
Cash and cash equivalents	0.0		0.0
Restricted cash	0.0		0.0
Total investments	587.0		736.0
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	24.0		(24.0)
Level 2 | Interest rate swap
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Derivatives	2.0		15.0
Level 3
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Cash and cash equivalents	0.0		0.0
Restricted cash	0.0		0.0
Total investments	26,091.0		22,084.0
Unfunded revolving and delayed draw loan commitments	(29.0)		(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	$ 9.0		$ 6.0

[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.