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INVESTMENTS - Ivy Hill Asset Management, L.P. (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
borrower
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
borrower
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Schedule of Investments [Line Items]          
Amortized cost of investments $ 29,477.5 [1]   $ 29,477.5 [1]   $ 29,249.9 [2]
Purchases of investments     8,033.0 $ 9,263.0  
Ivy Hill Asset Management, L.P.          
Schedule of Investments [Line Items]          
Purchases of investments     3,292.0 1,771.0  
Ivy Hill Asset Management, L.P.          
Schedule of Investments [Line Items]          
Assets under management $ 17,700.0   $ 17,700.0    
Number of borrowers | borrower 25   25    
Amortized cost of investments $ 3,863.0   $ 3,863.0   $ 3,190.0
Other income 2.0 $ 3.0 7.0 8.0  
Realized (loss) gain on sale of investments     (2.0) 0.0  
Ivy Hill Asset Management, L.P. | Ivy Hill Asset Management, L.P.          
Schedule of Investments [Line Items]          
Other income 16.0 15.0 46.0 39.0  
Other investment-related income $ 110.0 $ 86.0 $ 308.0 $ 199.0  
[1] As of September 30, 2026, the estimated net unrealized gain for federal tax purposes was approximately $0.1 billion based on a tax cost basis of approximately $29.3 billion. As of September 30, 2026, the estimated aggregate gross unrealized gain for federal income tax purposes was approximately $1.6 billion and the estimated aggregate gross unrealized loss for federal income tax purposes was approximately $1.5 billion.     
[2] 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.