Borrowings - Outstanding Debt Obligations (Details) SFr in Millions, $ in Millions, $ in Millions	Dec. 31, 2024 USD ($)	Dec. 31, 2024 EUR (€)	Dec. 31, 2024 GBP (£)	Dec. 31, 2024 CAD ($)	Dec. 31, 2024 CHF (SFr)	Dec. 31, 2024 AUD ($)	Dec. 11, 2024 USD ($)	Nov. 22, 2024 USD ($)	Sep. 26, 2024 USD ($)	May 29, 2024 USD ($)	Mar. 13, 2024 USD ($)	Jan. 25, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 EUR (€)	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 CAD ($)	Dec. 31, 2023 CHF (SFr)	Dec. 13, 2023 USD ($)	Nov. 27, 2023 USD ($)	Oct. 11, 2022 USD ($)	Sep. 27, 2022 USD ($)	Aug. 12, 2022 USD ($)	Jun. 09, 2022 USD ($)	May 03, 2022 USD ($)	Apr. 14, 2022 GBP (£)	Mar. 24, 2022 USD ($)	Jan. 18, 2022 USD ($)	Nov. 22, 2021 USD ($)	Nov. 02, 2021 EUR (€)	Nov. 01, 2021 USD ($)	Sep. 15, 2021 USD ($)	Aug. 17, 2021 USD ($)	Jun. 29, 2021 USD ($)	Jun. 21, 2021 USD ($)
Debt Instrument [Line Items]
Aggregate Principal Committed	$ 36,809,690,000												$ 35,719,459,000
Short-Term Debt	575,300,000												59,100,000
Total	30,708,757,000												23,407,827,000
Total	30,452,578,000												23,179,861,000
Net of unamortized debt issuance costs	136,810,000												91,634,000
Unused Portion	6,100,933,000												12,311,632,000
Amount Available	5,482,119,000												10,785,008,000
Bard Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,650,000,000												1,650,000,000
Outstanding Principal	1,000,298,000	€ 69,000,000	£ 74,600,000	$ 94.1									242,243,000	€ 69,000,000	£ 74,600,000	$ 94.1
Net Carrying Value	1,000,298,000												242,243,000
Unused Portion	649,702,000												1,407,757,000
Amount Available	559,732,000												1,290,994,000
Castle Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,900,000,000												1,600,000,000
Outstanding Principal	1,194,401,000	46,400,000	64,400,000	78.9									1,121,681,000	46,400,000	64,400,000	78.9
Net Carrying Value	1,194,401,000												1,121,681,000
Unused Portion	705,599,000												478,319,000
Amount Available	516,131,000												186,042,000
Summit Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,375,000,000												2,300,000,000
Outstanding Principal	952,105,000	26,900,000	99,700,000	64.7									286,046,000		101,700,000	160.6
Net Carrying Value	952,105,000												286,046,000
Unused Portion	422,895,000												2,013,954,000
Amount Available	422,895,000												1,575,278,000
Denali Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	750,000,000												750,000,000
Outstanding Principal	562,800,000												562,800,000
Net Carrying Value	562,800,000												562,800,000
Unused Portion	187,200,000												187,200,000
Amount Available	187,200,000												187,200,000
Bushnell Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	600,000,000												600,000,000
Outstanding Principal	480,300,000												465,300,000
Net Carrying Value	480,300,000												465,300,000
Unused Portion	119,700,000												134,700,000
Amount Available	119,700,000												134,512,000
Granite Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000												750,000,000
Outstanding Principal	493,554,000												563,600,000
Net Carrying Value	493,554,000												563,600,000
Unused Portion	6,446,000												186,400,000
Amount Available	6,446,000												86,337,000
Middle Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,000,000,000												1,000,000,000
Outstanding Principal	750,000,000												600,950,000
Net Carrying Value	750,000,000												600,950,000
Unused Portion	250,000,000												399,050,000
Amount Available	250,000,000												278,721,000
Bison Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,500,000,000												1,500,000,000
Outstanding Principal	1,203,200,000												703,200,000
Net Carrying Value	1,203,200,000												703,200,000
Unused Portion	296,800,000												796,800,000
Amount Available	296,800,000												796,800,000
Blanca Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,500,000,000												1,500,000,000
Outstanding Principal	1,375,090,000												1,375,090,000
Net Carrying Value	1,375,090,000												1,375,090,000
Unused Portion	124,910,000												124,910,000
Amount Available	65,207,000												124,910,000
Windom Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	2,150,000,000												2,150,000,000
Outstanding Principal	1,029,841,000		115,900,000										967,477,000		115,900,000
Net Carrying Value	1,029,841,000												967,477,000
Unused Portion	1,120,159,000												1,182,523,000
Amount Available	1,120,159,000												1,182,505,000
Monarch Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	1,500,000,000												2,000,000,000
Outstanding Principal	750,000,000												1,400,400,000
Net Carrying Value	750,000,000												1,400,400,000
Unused Portion	750,000,000												599,600,000
Amount Available	534,195,000												330,688,000
Meridian Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	350,000,000												350,000,000
Outstanding Principal	246,000,000												246,000,000
Net Carrying Value	246,000,000												246,000,000
Unused Portion	104,000,000												104,000,000
Amount Available	104,000,000												104,000,000
Haydon Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	250,000,000												250,000,000
Outstanding Principal	250,000,000												49,000,000
Net Carrying Value	250,000,000												49,000,000
Unused Portion	0												201,000,000
Amount Available	0												201,000,000
Bear Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	517,925,000	500,000,000.0											551,975,000
Outstanding Principal	164,816,000	110,800,000	40,000,000										360,531,000	260,800,000	57,000,000
Net Carrying Value	164,816,000												360,531,000
Unused Portion	353,109,000												191,444,000
Amount Available	289,286,000												191,444,000
Phoenix Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	197,736,000
Outstanding Principal	197,736,000	142,800,000	39,800,000
Net Carrying Value	197,736,000
Unused Portion	0
Amount Available	0
Revolving Credit Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed	5,650,000,000												5,150,000,000
Outstanding Principal	4,639,587,000	€ 850,000,000	£ 1,108,300,000	$ 816.0	SFr 52.9	$ 1.0							1,131,025,000	€ 8,000,000	£ 445,700,000	$ 134.0	SFr 52.9
Net Carrying Value	4,639,587,000												1,131,025,000
Unused Portion	1,010,413,000												4,018,975,000
Amount Available	1,010,368,000												4,018,453,000
June 2026 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	400,000,000												400,000,000																			$ 400,000,000.0
Outstanding Principal	400,000,000												400,000,000
Net Carrying Value	398,930,000												398,270,000
Net of unamortized debt issuance costs	1,070,000												1,730,000
May 2027 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	625,000,000												625,000,000											$ 625,000,000.0
Outstanding Principal	625,000,000												625,000,000
Net Carrying Value	606,940,000												605,332,000
Net of unamortized debt issuance costs	1,293,000												1,848,000
October 2027 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	350,000,000												350,000,000							$ 350,000,000.0
Outstanding Principal	350,000,000												350,000,000
Net Carrying Value	343,257,000												345,621,000
Net of unamortized debt issuance costs	3,826,000												5,209,000
December 2026 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	1,250,000,000												1,250,000,000																		$ 900,000,000.0
Outstanding Principal	1,250,000,000												1,250,000,000
Net Carrying Value	1,200,860,000												1,187,236,000
Net of unamortized debt issuance costs	9,414,000												14,265,000
November 2026 Eurobonds | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	517,925,000												551,975,000																€ 500,000,000.0
Outstanding Principal	517,925,000												551,975,000
Net Carrying Value	514,940,000												547,426,000
Net of unamortized debt issuance costs	2,984,000												4,549,000
March 2027 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	1,000,000,000												1,000,000,000															$ 1,000,000,000.0
Outstanding Principal	1,000,000,000												1,000,000,000
Net Carrying Value	994,032,000												991,311,000
Net of unamortized debt issuance costs	5,968,000												8,689,000
January 2025 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000												500,000,000														$ 500,000,000.0
Outstanding Principal	500,000,000												500,000,000
Net Carrying Value	499,806,000												483,230,000
Net of unamortized debt issuance costs	65,000												1,796,000
January 2029 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	650,000,000												650,000,000														$ 650,000,000.0
Outstanding Principal	650,000,000												650,000,000
Net Carrying Value	642,805,000												641,028,000
Net of unamortized debt issuance costs	7,195,000												8,972,000
March 2025 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	900,000,000												900,000,000													$ 900,000,000.0
Outstanding Principal	900,000,000												900,000,000
Net Carrying Value	895,447,000												871,800,000
Net of unamortized debt issuance costs	658,000												3,596,000
April 2026 UK Bonds | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	312,975,000												318,663,000												£ 250,000,000.0
Outstanding Principal	312,975,000												318,663,000
Net Carrying Value	303,118,000												304,284,000
Net of unamortized debt issuance costs	1,128,000												2,010,000
September 2025 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	800,000,000												800,000,000								$ 600,000,000.0
Outstanding Principal	800,000,000												800,000,000
Net Carrying Value	796,012,000												790,713,000
Net of unamortized debt issuance costs	3,183,000												7,471,000
November 2028 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000												500,000,000						$ 500,000,000.0
Outstanding Principal	500,000,000												500,000,000
Net Carrying Value	491,884,000												501,424,000
Net of unamortized debt issuance costs	9,315,000												11,536,000
January 2031 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000											$ 500,000,000.0
Outstanding Principal	500,000,000
Net Carrying Value	478,572,000
Net of unamortized debt issuance costs	12,752,000
July 2029 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	500,000,000									$ 500,000,000.0
Outstanding Principal	500,000,000
Net Carrying Value	492,483,000
Net of unamortized debt issuance costs	10,248,000
September 2027 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	400,000,000								$ 400,000,000.0
Outstanding Principal	400,000,000
Net Carrying Value	385,192,000
Net of unamortized debt issuance costs	5,989,000
April 2030 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	400,000,000								$ 400,000,000.0
Outstanding Principal	400,000,000
Net Carrying Value	374,785,000
Net of unamortized debt issuance costs	8,969,000
November 2029 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	400,000,000							$ 400,000,000.0
Outstanding Principal	400,000,000
Net Carrying Value	389,112,000
Net of unamortized debt issuance costs	8,737,000
November 2034 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	800,000,000						$ 200,000,000.0	$ 600,000,000.0
Outstanding Principal	800,000,000
Net Carrying Value	761,812,000
Net of unamortized debt issuance costs	23,750,000
2021-1 BSL Notes
Debt Instrument [Line Items]
Outstanding Principal	819,500,000
2021-1 BSL Notes | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	663,000,000												663,000,000																				$ 876,600,000
Outstanding Principal	663,000,000												663,000,000
Net Carrying Value	662,170,000												662,083,000
Net of unamortized debt issuance costs	830,000												917,000
2021-2 Notes
Debt Instrument [Line Items]
Outstanding Principal	603,650,000
2021-2 Notes | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	505,800,000												505,800,000																	$ 603,700,000
Outstanding Principal	505,800,000												505,800,000
Net Carrying Value	504,516,000												504,385,000
Net of unamortized debt issuance costs	1,284,000												1,415,000
MML 2021-1 Debt | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	690,000,000												690,000,000
Outstanding Principal	690,000,000												690,000,000
Net Carrying Value	686,473,000												686,121,000
Net of unamortized debt issuance costs	3,527,000												3,879,000
MML 2022-1 Debt | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	759,000,000												759,000,000
Outstanding Principal	759,000,000												759,000,000
Net Carrying Value	754,464,000												754,024,000
Net of unamortized debt issuance costs	4,536,000												4,976,000
2022-1 BSL Debt
Debt Instrument [Line Items]
Outstanding Principal	589,750,000
2022-1 BSL Debt | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	420,000,000												420,000,000										$ 589,800,000
Outstanding Principal	531,000,000
Outstanding Principal, Net of Eliminations	420,000,000												420,000,000
Net Carrying Value	418,661,000												418,534,000
Net of unamortized debt issuance costs	1,339,000												1,466,000
MML 2022-2 Debt
Debt Instrument [Line Items]
Outstanding Principal	498,105,000																					$ 498,100,000
MML 2022-2 Debt | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	300,500,000												300,500,000
Outstanding Principal	341,000,000
Outstanding Principal, Net of Eliminations	300,500,000												300,500,000
Net Carrying Value	298,280,000												298,046,000
Net of unamortized debt issuance costs	2,220,000												2,454,000
2023-1 Notes
Debt Instrument [Line Items]
Outstanding Principal	492,665,000																	$ 492,700,000
2023-1 Notes | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	305,000,000												305,000,000
Outstanding Principal	339,000,000
Outstanding Principal, Net of Eliminations	305,000,000												305,000,000
Net Carrying Value	303,206,000												303,044,000
Net of unamortized debt issuance costs	1,794,000												1,956,000
Naomi Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed													400,000,000
Outstanding Principal													385,000,000
Net Carrying Value													385,000,000
Unused Portion													15,000,000
Amount Available													15,000,000
June 2024 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed													435,000,000																					$ 435,000,000.0
Outstanding Principal													435,000,000
Net Carrying Value													426,970,000
Net of unamortized debt issuance costs													612,000
Borah Peak Funding Facility | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed													400,000,000
Outstanding Principal													130,000,000
Net Carrying Value													130,000,000
Unused Portion													270,000,000
Amount Available													81,124,000
September 2024 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed													365,000,000																		$ 365,000,000.0
Outstanding Principal													365,000,000
Net Carrying Value													355,524,000
Net of unamortized debt issuance costs													834,000
2024-1 Notes
Debt Instrument [Line Items]
Outstanding Principal	402,161,000										$ 402,200,000
2024-1 Notes | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	244,000,000
Outstanding Principal	272,000,000
Outstanding Principal, Net of Eliminations	244,000,000
Net Carrying Value	242,337,000
Net of unamortized debt issuance costs	1,663,000
2024-2 Notes
Debt Instrument [Line Items]
Outstanding Principal	500,500,000						$ 500,500,000
2024-2 Notes | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	305,000,000
Outstanding Principal	340,000,000
Outstanding Principal, Net of Eliminations	305,000,000
Net Carrying Value	301,927,000
Net of unamortized debt issuance costs	3,073,000
Short-Term Borrowings
Debt Instrument [Line Items]
Aggregate Principal Committed	420,829,000												28,546,000
Short-Term Debt	$ 420,829,000												28,546,000
November 2024 Notes | Unsecured debt
Debt Instrument [Line Items]
Aggregate Principal Committed													500,000,000															$ 500,000,000.0
Outstanding Principal													500,000,000
Net Carrying Value													484,566,000
Net of unamortized debt issuance costs													$ 1,454,000