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Investments - SLP (Details) - USD ($)													3 Months Ended	6 Months Ended
Investments - SLP (Details) - USD ($)	Apr. 06, 2026	Aug. 13, 2025	Jul. 08, 2025	Dec. 09, 2024	Jul. 10, 2024	Mar. 13, 2024	Sep. 27, 2023	Jun. 15, 2023	Aug. 24, 2022	Mar. 07, 2022	Feb. 09, 2022	Nov. 30, 2021	Jun. 30, 2026	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025	May 20, 2024	Aug. 09, 2023
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investments sold											$ 2,551,200,000		$ 65,200,000	$ 167,800,000
Investments purchased											$ 102,500,000		0	0
Proceeds from principal payments and sales of investments														488,991,000	$ 751,100,000
Maximum borrowing capacity																	$ 1,500,000,000
Total aggregate principal amount committed													$ 2,127,000,000	$ 2,127,000,000		$ 2,077,000,000
Weighted average interest rate of debt (as a percent)													4.80%	4.80%		4.80%
2018-1 Notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Net realized loss on extinguishment of debt						$ (1,300,000)
2018-1 Notes \| Membership Interests [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Total aggregate principal amount committed						22,400,000
2023-1 Notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Term Debt Secuiritisation																		$ 400,000,000
2024-1 Notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Term Debt Secuiritisation					$ 450,400,000
2025-1 Notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Term Debt Secuiritisation			$ 349,100,000
Class BR senior deferrable floating rate notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Debt instrument retained												$ 32,500,000
Total aggregate principal amount committed												47,500,000
Class CR senior deferrable floating rate notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Debt instrument retained												25,000,000
Total aggregate principal amount committed												$ 25,000,000
BCC Middle Market CLO 20181 LLC \| 2018-1 Notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)								0.26%
Investment, Variable Interest Rate, Type [Extensible Enumeration]								us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Bain Capital Senior Loan Program, LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Subordinated notes													$ 163,800,000	$ 163,800,000		$ 157,900,000
Total aggregate principal amount committed	$ 446,000,000	$ 331,600,000				$ 500,000,000
Weighted average interest rate of debt (as a percent)													5.90%	5.90%		6.90%
Bain Capital Senior Loan Program, LLC \| M M 22 2 Credit Facility [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Maximum borrowing capacity									$ 225,000,000
Spread rate (as a percent)									2.10%
Investment, Variable Interest Rate, Type [Extensible Enumeration]									us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Bain Capital Senior Loan Program, LLC \| M M 23 3 Credit Facility [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Maximum borrowing capacity							$ 140,000,000
Spread rate (as a percent)							2.85%
Investment, Variable Interest Rate, Type [Extensible Enumeration]							us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Bain Capital Senior Loan Program, LLC \| MM CLO WH 3 Credit Facility [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Maximum borrowing capacity				$ 300,000,000
Spread rate (as a percent)				200.00%
Investment, Variable Interest Rate, Type [Extensible Enumeration]				us-gaap:SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Bain Capital Senior Loan Program, LLC \| Preferred Stock [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investments at fair value													$ 1,800,000	$ 1,800,000		$ 1,800,000
Bain Capital Senior Loan Program, LLC \| Common Stock [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Equity interests													$ 0	$ 0		$ 5,000,000
Bain Capital Senior Loan Program, LLC \| 2018-1 Notes \| Membership Interests [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Total aggregate principal amount committed	$ 87,700,000
Bain Capital Senior Loan Program, LLC \| 2023-1 Notes \| Membership Interests [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investment membership interest		$ 45,600,000
Debt instrument percentage of interest retained		100.00%
Bain Capital Senior Loan Program, LLC \| 2024-1 Notes \| Membership Interests [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investment membership interest					$ 76,400,000
Debt instrument percentage of interest retained					100.00%
Bain Capital Senior Loan Program, LLC \| 2025-1 Notes \| Membership Interests [Member]
Investment Company, Nonconsolidated Subsidiary [Line Items]
Investment membership interest			$ 53,400,000
Debt instrument percentage of interest retained			100.00%
Bain Capital Senior Loan Program, LLC \| Class A-1-L
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	1.67%
Total aggregate principal amount committed	$ 150,000,000
Bain Capital Senior Loan Program, LLC \| Class A-1-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	1.67%	1.58%				2.25%
Total aggregate principal amount committed	$ 140,000,000	$ 188,500,000				$ 290,000,000
Bain Capital Senior Loan Program, LLC \| Class A-J-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	1.90%					2.70%
Total aggregate principal amount committed	$ 20,000,000					$ 20,000,000
Bain Capital Senior Loan Program, LLC \| Class A-2-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	2.05%	1.80%				2.90%
Total aggregate principal amount committed	$ 17,000,000	$ 9,800,000				$ 30,000,000
Bain Capital Senior Loan Program, LLC \| Class A-2-FR
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	5.81%
Total aggregate principal amount committed	$ 13,000,000
Bain Capital Senior Loan Program, LLC \| Class B-F-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	6.78%
Total aggregate principal amount committed	$ 5,000,000
Bain Capital Senior Loan Program, LLC \| Class B-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	3.00%					3.90%
Total aggregate principal amount committed	$ 35,000,000					$ 40,000,000
Bain Capital Senior Loan Program, LLC \| Class C-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	4.71%					5.90%
Total aggregate principal amount committed	$ 30,000,000					$ 30,000,000
Bain Capital Senior Loan Program, LLC \| Class D-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	7.70%					8.32%
Total aggregate principal amount committed	$ 30,000,000					$ 30,000,000
Bain Capital Senior Loan Program, LLC \| Class X-R-R
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)	1.10%
Total aggregate principal amount committed	$ 6,000,000
Bain Capital Senior Loan Program, LLC \| Class BR senior deferrable floating rate notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)		1.90%
Total aggregate principal amount committed		$ 22,800,000
Bain Capital Senior Loan Program, LLC \| Class CR senior deferrable floating rate notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)		2.25%
Debt instrument retained		$ 19,600,000
Total aggregate principal amount committed		$ 27,600,000
Bain Capital Senior Loan Program, LLC \| Class DR senior deferrable floating rate notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)		3.25%
Total aggregate principal amount committed		$ 17,900,000
Bain Capital Senior Loan Program, LLC \| Class ER senior deferrable floating rate notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Spread rate (as a percent)		6.50%
Debt instrument retained		$ 19,500,000
Total aggregate principal amount committed		$ 19,500,000
Bain Capital Senior Loan Program, LLC \| Class E notes
Investment Company, Nonconsolidated Subsidiary [Line Items]
Debt instrument retained					$ 25,500,000
Bain Capital Senior Loan Program, LLC \| BCC Middle Market CLO 20181 LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Membership equity interest acquired										70.00%	70.00%
Membership interests (as a percent)										30.00%	30.00%
Proceeds from principal payments and sales of investments										$ 56,100,000
Net realized gain from sale of investment										$ 1,200,000
Amberstone Co., Ltd. \| Bain Capital Senior Loan Program, LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Economic ownership interest											50.00%
Initial capital contributions											$ 179,000,000