Fair Value of Financial Instruments - Unobservable Inputs (Details) $ in Millions	Dec. 31, 2024 USD ($)		Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 13,490.4	[1],[2]	$ 14,649.3	[3],[4]
Level 3—Significant unobservable inputs
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	12,035.0		13,073.0
Level 3—Significant unobservable inputs | Senior Debt | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 7,115.0		$ 8,356.0
Level 3—Significant unobservable inputs | Senior Debt | Discounted Cash Flow | Discount Rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.058		0.061
Level 3—Significant unobservable inputs | Senior Debt | Discounted Cash Flow | Discount Rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.238		0.250
Level 3—Significant unobservable inputs | Senior Debt | Discounted Cash Flow | Discount Rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.106		0.116
Level 3—Significant unobservable inputs | Senior Debt | Waterfall
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 1,376.0		$ 1,165.0
Level 3—Significant unobservable inputs | Senior Debt | Waterfall | EBITDA Multiple | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.7		0.6
Level 3—Significant unobservable inputs | Senior Debt | Waterfall | EBITDA Multiple | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	11.3		10.8
Level 3—Significant unobservable inputs | Senior Debt | Waterfall | EBITDA Multiple | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	8.6		8.1
Level 3—Significant unobservable inputs | Senior Debt | Other
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 14.0		$ 4.0
Level 3—Significant unobservable inputs | Senior Debt | Cost
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	14.0		15.0
Level 3—Significant unobservable inputs | Subordinated Debt | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 188.0		$ 289.0
Level 3—Significant unobservable inputs | Subordinated Debt | Discounted Cash Flow | Discount Rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.113		0.107
Level 3—Significant unobservable inputs | Subordinated Debt | Discounted Cash Flow | Discount Rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.154		0.210
Level 3—Significant unobservable inputs | Subordinated Debt | Discounted Cash Flow | Discount Rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.127		0.137
Level 3—Significant unobservable inputs | Subordinated Debt | Waterfall
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 33.0		$ 33.0
Level 3—Significant unobservable inputs | Subordinated Debt | Waterfall | EBITDA Multiple | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	7.0		7.5
Level 3—Significant unobservable inputs | Subordinated Debt | Waterfall | EBITDA Multiple | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	7.0		7.5
Level 3—Significant unobservable inputs | Subordinated Debt | Waterfall | EBITDA Multiple | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	7.0		7.5
Level 3—Significant unobservable inputs | Subordinated Debt | Other
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 12.0
Level 3—Significant unobservable inputs | Asset Based Finance | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 1,513.0		$ 1,232.0
Level 3—Significant unobservable inputs | Asset Based Finance | Discounted Cash Flow | Discount Rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.048		0.059
Level 3—Significant unobservable inputs | Asset Based Finance | Discounted Cash Flow | Discount Rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.417		0.432
Level 3—Significant unobservable inputs | Asset Based Finance | Discounted Cash Flow | Discount Rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.128		0.111
Level 3—Significant unobservable inputs | Asset Based Finance | Waterfall
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 516.0		$ 616.0
Level 3—Significant unobservable inputs | Asset Based Finance | Waterfall | EBITDA Multiple | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	1.0		1.0
Level 3—Significant unobservable inputs | Asset Based Finance | Waterfall | EBITDA Multiple | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	1.4		1.3
Level 3—Significant unobservable inputs | Asset Based Finance | Waterfall | EBITDA Multiple | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	1.2		1.1
Level 3—Significant unobservable inputs | Asset Based Finance | Other
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 30.0		$ 109.0
Level 3—Significant unobservable inputs | Asset Based Finance | Cost
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	41.0		118.0
Level 3—Significant unobservable inputs | Asset Based Finance | Indicative Dealer Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 2.0		$ 2.0
Level 3—Significant unobservable inputs | Asset Based Finance | Indicative Dealer Quotes | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.230		0.268
Level 3—Significant unobservable inputs | Asset Based Finance | Indicative Dealer Quotes | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.230		0.268
Level 3—Significant unobservable inputs | Asset Based Finance | Indicative Dealer Quotes | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.230		0.268
Level 3—Significant unobservable inputs | Equity/Other | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 538.0		$ 521.0
Level 3—Significant unobservable inputs | Equity/Other | Discounted Cash Flow | Discount Rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.043		0.052
Level 3—Significant unobservable inputs | Equity/Other | Discounted Cash Flow | Discount Rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.248		0.210
Level 3—Significant unobservable inputs | Equity/Other | Discounted Cash Flow | Discount Rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.143		0.142
Level 3—Significant unobservable inputs | Equity/Other | Waterfall
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 625.0		$ 603.0
Level 3—Significant unobservable inputs | Equity/Other | Waterfall | EBITDA Multiple | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	0.7		0.6
Level 3—Significant unobservable inputs | Equity/Other | Waterfall | EBITDA Multiple | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	16.0		14.8
Level 3—Significant unobservable inputs | Equity/Other | Waterfall | EBITDA Multiple | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input	8.3		6.5
Level 3—Significant unobservable inputs | Equity/Other | Other
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value			$ 7.0
Level 3—Significant unobservable inputs | Equity/Other | Cost
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value	$ 18.0
Level 3—Significant unobservable inputs | Equity/Other | Option Pricing Model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, at fair value			$ 3.0
Level 3—Significant unobservable inputs | Equity/Other | Option Pricing Model | Equity Illiquidity Discount | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input			0.750
Level 3—Significant unobservable inputs | Equity/Other | Option Pricing Model | Equity Illiquidity Discount | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input			0.750
Level 3—Significant unobservable inputs | Equity/Other | Option Pricing Model | Equity Illiquidity Discount | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment owned, measurement input			0.750

[1] See Note 8 for additional information regarding the fair value of the Company’s financial instruments.

[2] Security may be an obligation of one or more entities affiliated with the named company.

[3] See Note 8 for additional information regarding the fair value of the Company’s financial instruments.

[4] Security may be an obligation of one or more entities affiliated with the named company.