Fair Value of Financial Instruments - Fair Value Hierarchy (Details) - USD ($) $ in Millions	Dec. 31, 2022		Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	$ 15,377.3	[1]	$ 16,101.5	[2]
Level 1—Price quotations in active markets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	0.0		30.0
Level 2—Significant other observable inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	564.0		703.0
Level 3—Significant unobservable inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	13,385.0		13,972.0
Investments measured at net asset value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value	$ 1,428.0		$ 1,396.0

[1] Fair value determined by the Company’s board of directors (see Note 8).

[2] Fair value determined by the Company’s board of directors (see Note 8).