BORROWINGS - July 2026 Notes (Details) - Senior Notes - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	May 10, 2022	Jul. 29, 2021
MassMutual
Debt Instrument [Line Items]
Aggregate principal amount				$ 46.0
July 29, 2021 – Series A Notes
Debt Instrument [Line Items]
Aggregate principal amount				75.0
Fixed interest rate	3.50%
September 15, 2021 – Series B Notes
Debt Instrument [Line Items]
Aggregate principal amount				38.0
Fixed interest rate	3.50%
October 28, 2021 – Series C Notes
Debt Instrument [Line Items]
Aggregate principal amount				$ 37.0
Fixed interest rate	3.50%
July 2026 Unsecured Notes
Debt Instrument [Line Items]
Fixed interest rate				3.50%
Total assets threshold				0.0150
July 2026 Unsecured Notes | Level 3
Debt Instrument [Line Items]
Long term debt fair value	$ 147.3	$ 142.0
July 2026 Unsecured Notes | External Credit Rating, Investment Grade
Debt Instrument [Line Items]
Investment grade conditions				0.0075
May 2027 Unsecured Notes
Debt Instrument [Line Items]
Fixed interest rate			6.00%
Investment grade conditions			0.0075
Total assets threshold			0.0150
May 2027 Unsecured Notes | Level 3
Debt Instrument [Line Items]
Long term debt fair value	$ 155.2	$ 149.9