Borrowings - Debt Securitizations (Details) - USD ($)		9 Months Ended
	Jun. 29, 2021	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Aug. 12, 2022	Jun. 09, 2022	Mar. 15, 2022	Dec. 15, 2021	Nov. 01, 2021
Debt Instrument [Line Items]
Aggregate Principal Committed		$ 34,855,746,000		$ 36,037,871,000
Borrowings on debt		2,610,921,000	$ 17,575,191,000
2021-1 BSL Debt
Debt Instrument [Line Items]
Outstanding Principal		819,500,000
2021-1 BSL Debt | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	$ 876,600,000	663,000,000		663,000,000
Borrowings on debt	819,500,000
Outstanding Principal		663,000,000		663,000,000
2021-1 BSL Debt | Subordinated Debt
Debt Instrument [Line Items]
Outstanding Principal		156,500,000
2021-1 BSL, Senior Secured Floating Rate, Class A Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 499,800,000
2021-1 BSL, Senior Secured Floating Rate, Class A Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.25%
2021-1 BSL, Senior Secured Floating Rate, Class B Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 38,760,000
2021-1 BSL, Senior Secured Floating Rate, Class B Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.80%
2021-1 BSL, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 59,160,000
2021-1 BSL, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.15%
2021-1 BSL, Mezzanine Secured Deferrable Floating Rate, Class D Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 65,280,000
2021-1 BSL, Mezzanine Secured Deferrable Floating Rate, Class D Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		3.35%
2021-1 BSL, Junior Secured Deferrable Floating Rate | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed	$ 57,100,000
Outstanding Principal		$ 0
2021-1 BSL, Junior Secured Deferrable Floating Rate | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		7.00%
2021-2 Debt
Debt Instrument [Line Items]
Outstanding Principal		$ 603,650,000
2021-2 Debt | 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
2021-2 Debt | Subordinated Debt
Debt Instrument [Line Items]
Outstanding Principal		97,850,000
2021-2 Debt, Senior Secured Floating Rate, Class A-L Loans | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 218,000,000
2021-2 Debt, Senior Secured Floating Rate, Class A-L Loans | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.22%
2021-2 Debt, Senior Secured Floating Rate, Class A Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 149,500,000
2021-2 Debt, Senior Secured Floating Rate, Class A Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.22%
2021-2 Notes, Senior Secured Floating Rate, Class B Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 38,100,000
2021-2 Notes, Senior Secured Floating Rate, Class B Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.75%
2021-2 Notes, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 48,000,000
2021-2 Notes, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.05%
2021-2 Notes, Mezzanine Secured Deferrable Floating Rate, Class D Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 52,200,000
2021-2 Notes, Mezzanine Secured Deferrable Floating Rate, Class D Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		3.15%
2021-1 MML Debt
Debt Instrument [Line Items]
Outstanding Principal		$ 1,001,000,000
2021-1 MML Debt | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed								$ 1,001,000,000
Outstanding Principal		690,000,000
2021-1 MML Debt | Subordinated Debt
Debt Instrument [Line Items]
Outstanding Principal		311,000,000
2021-1 MML Debt, Senior Secured Floating Rate, Class A Loans | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 50,000,000
2021-1 MML Debt, Senior Secured Floating Rate, Class A Loans | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.48%
2021-1 MML Debt, Senior Secured Floating Rate, Class A Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 480,000,000
2021-1 MML Debt, Senior Secured Floating Rate, Class A Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.48%
2021-1 MML Debt, Senior Secured Floating Rate, Class B Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 80,000,000
2021-1 MML Debt, Senior Secured Floating Rate, Class B Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.90%
2021-1 MML Debt, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 80,000,000
2021-1 MML Debt, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.60%
2022-1 MML Debt
Debt Instrument [Line Items]
Outstanding Principal		$ 1,090,360,000
2022-1 MML Debt | Secured debt
Debt Instrument [Line Items]
Aggregate Principal Committed							$ 1,090,000,000.00
Outstanding Principal		759,000,000
2022-1 MML Debt | Subordinated Debt
Debt Instrument [Line Items]
Outstanding Principal		331,360,000
2022-1 MML Debt, Senior Secured Floating Rate, Class A-1 Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 525,000,000
2022-1 MML Debt, Senior Secured Floating Rate, Class A-1 Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.65%
2022-1 MML Debt, Senior Secured Fixed, Class A-2 Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 80,000,000
Interest rate		3.41%
2022-1 MML Debt, Senior Secured Floating Rate, Class B Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 66,000,000
2022-1 MML Debt, Senior Secured Floating Rate, Class B Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.00%
2022-1 MML Debt, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 88,000,000
2022-1 MML Debt, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.75%
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		$ 589,750,000
Outstanding Principal		531,000,000
2022-1 BSL Debt | Subordinated Debt
Debt Instrument [Line Items]
Outstanding Principal		58,750,000
2022-1 BSL Debt, Senior Secured Floating Rate, Class A-1A Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 292,000,000
2022-1 BSL Debt, Senior Secured Floating Rate, Class A-1A Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		1.58%
2022-1 BSL Debt, Senior Secured Fixed Rate, Class A-1B Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 50,000,000
Interest rate		4.34%
2022-1 BSL Debt, Senior Secured Floating Rate, Class A-2 Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 12,000,000
2022-1 BSL Debt, Senior Secured Floating Rate, Class A-2 Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.00%
2022-1 BSL Debt, Senior Secured Floating Rate, Class B-1 Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 40,000,000
2022-1 BSL Debt, Senior Secured Floating Rate, Class B-1 Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.35%
2022-1 BSL Debt, Senior Secured Fixed Rate, Class B-2 Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 26,000,000
Interest rate		4.98%
2022-1 BSL Debt, Secured Deferrable Floating Rate, Class C Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 51,000,000
2022-1 BSL Debt, Secured Deferrable Floating Rate, Class C Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.60%
2022-1 BSL Debt, Mezzanine Secured Deferrable Floating Rate, Class D Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 39,000,000
2022-1 BSL Debt, Mezzanine Secured Deferrable Floating Rate, Class D Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		3.69%
2022-1 BSL Debt, Mezzanine Secured Deferrable Floating Rate, Class E Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 21,000,000
2022-1 BSL Debt, Mezzanine Secured Deferrable Floating Rate, Class E Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		7.33%
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
MML 2022-2 Debt | Subordinated Debt
Debt Instrument [Line Items]
Outstanding Principal		157,105,000
MML 2022-2 Debt, Senior Secured Floating Rate, Class A-L Loans | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 275,000,000
MML 2022-2 Debt, Senior Secured Floating Rate, Class A-L Loans | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.10%
MML 2022-2 Debt, Senior Secured Floating Rate, Class B-1 Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 14,000,000
MML 2022-2 Debt, Senior Secured Floating Rate, Class B-1 Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		3.35%
MML 2022-2 Debt, Senior Secured Fixed Rate, Class B-2 Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 11,500,000
Interest rate		5.88%
MML 2022-2 Debt, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt
Debt Instrument [Line Items]
Outstanding Principal		$ 40,500,000
MML 2022-2 Debt, Mezzanine Secured Deferrable Floating Rate, Class C Notes | Secured debt | SOFR
Debt Instrument [Line Items]
Applicable margin rate		2.50%