INVESTMENTS - Other Invested Assets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	$ 341	$ 211
Retained Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	112	85
Ceded Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	229	126
Derivative instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	238	117
Derivative instruments | Retained Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	16	0
Derivative instruments | Ceded Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	222	117
Other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	68	61
Other | Retained Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	68	61
Other | Ceded Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	0	0
Partnership Interest | Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	35	33
Partnership Interest | Retained Business | Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	28	24
Partnership Interest | Ceded Business | Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	7	9
Partnership Interest | Private equity | Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	29	24
Partnership Interest | Private equity | Retained Business | Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	28	24
Partnership Interest | Private equity | Ceded Business | Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	1	0
Partnership Interest | Equity Method Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	6	9
Partnership Interest | Equity Method Investments | Retained Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	0	0
Partnership Interest | Equity Method Investments | Ceded Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	6	9
Partnership Interest | Equity Method Investments | Private equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	3	4
Partnership Interest | Equity Method Investments | Private equity | Retained Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	0	0
Partnership Interest | Equity Method Investments | Private equity | Ceded Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	3	4
Partnership Interest | Equity Method Investments | Real estate-related
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	3	5
Partnership Interest | Equity Method Investments | Real estate-related | Retained Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	0	0
Partnership Interest | Equity Method Investments | Real estate-related | Ceded Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total other invested assets	$ 3	$ 5