DERIVATIVE INSTRUMENTS - Narrative (Details) - Derivative instruments not designated as hedges - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Interest rate futures | Long
Derivative [Line Items]
Notional amount	$ 2,200,000,000	$ 2,400,000,000
Interest rate futures | Short
Derivative [Line Items]
Notional amount	1,500,000,000	500,000,000
Foreign currency forward contracts, underwriting and non-investment operations | Long
Derivative [Line Items]
Notional amount	763,600,000	861,700,000
Foreign currency forward contracts, underwriting and non-investment operations | Short
Derivative [Line Items]
Notional amount	151,000,000	172,400,000
Foreign currency forward contracts, investment operations | Long
Derivative [Line Items]
Notional amount	339,100,000	225,600,000
Foreign currency forward contracts, investment operations | Short
Derivative [Line Items]
Notional amount	75,800,000	86,300,000
Credit default swaps | Long
Derivative [Line Items]
Notional amount	19,500,000	953,400,000
Credit default swaps | Short
Derivative [Line Items]
Notional amount	1,000,000,000	13,100,000
Total return swaps
Derivative [Line Items]
Notional amount	0	0
Equity futures | Long
Derivative [Line Items]
Notional amount		$ 116,000,000
Equity futures | Short
Derivative [Line Items]
Notional amount	$ 0