Fair Value Measurements - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 48,413,196	$ 48,908,608
Level 1, Level 2, and Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	46,261,807	46,720,214
Level 1, Level 2, and Level 3 | First lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	43,280,219	43,710,812
Level 1, Level 2, and Level 3 | Second lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,779,485	1,872,806
Level 1, Level 2, and Level 3 | Unsecured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	13,948
Level 1, Level 2, and Level 3 | Structured finance obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	395,026	365,269
Level 1, Level 2, and Level 3 | Equity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	807,077	757,379
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 1 | First lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 1 | Second lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 1 | Unsecured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 1 | Structured finance obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 1 | Equity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	5,175,644	6,973,233
Level 2 | First lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	4,381,443	6,167,268
Level 2 | Second lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	720,643	720,083
Level 2 | Unsecured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	13,948
Level 2 | Structured finance obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	73,558	71,934
Level 2 | Equity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	41,086,163	39,746,981
Level 3 | First lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	38,898,776	37,543,544
Level 3 | Second lien debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,058,842	1,152,723
Level 3 | Unsecured debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Level 3 | Structured finance obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	321,468	293,335
Level 3 | Equity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	807,077	757,379
NAV
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 2,151,389	$ 2,188,394