FAIR VALUE DISCLOSURES - Fair Value Measurement Reconciliation For All Levels (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Realized and unrealized gains (losses), included in Net income (loss) as:
Net derivative gains (losses)	$ (1,000,000)	$ (5,000,000)
Transfers into Level 3	0	0
Transfers out of Level 3	0	(10,000,000)
Level 3 | Corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	87,000,000	18,000,000
Realized and unrealized gains (losses), included in Net income (loss) as:
Investment gains (losses), reported in net investment income	0	0
Net derivative gains (losses)	0	0
Total realized and unrealized gains (losses)	0	0
Other comprehensive income (loss)	0	0
Purchases	15,000,000	29,000,000
Sales	(2,000,000)	0
Change in fair value of funds withheld assets	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(10,000,000)
Closing Balance	100,000,000	37,000,000
Change in unrealized gains or losses for the period included in earnings for instruments held at the end of the reporting period	0	0
Change in unrealized gains or losses for the period included in other comprehensive income for instruments held at the end of the reporting period.	0	0
Level 3 | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	24,000,000	0
Realized and unrealized gains (losses), included in Net income (loss) as:
Investment gains (losses), reported in net investment income	0	0
Net derivative gains (losses)	0	0
Total realized and unrealized gains (losses)	0	0
Other comprehensive income (loss)	0	0
Purchases	25,000,000	0
Sales	(11,000,000)	0
Change in fair value of funds withheld assets
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Closing Balance	38,000,000	0
Change in unrealized gains or losses for the period included in earnings for instruments held at the end of the reporting period	0	0
Change in unrealized gains or losses for the period included in other comprehensive income for instruments held at the end of the reporting period.	0	0
Level 3 | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,000,000	0
Realized and unrealized gains (losses), included in Net income (loss) as:
Investment gains (losses), reported in net investment income	0	0
Net derivative gains (losses)	0	0
Total realized and unrealized gains (losses)	0	0
Other comprehensive income (loss)	0	0
Purchases	0	0
Sales	0	0
Change in fair value of funds withheld assets	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Closing Balance	1,000,000	0
Change in unrealized gains or losses for the period included in earnings for instruments held at the end of the reporting period	0	0
Change in unrealized gains or losses for the period included in other comprehensive income for instruments held at the end of the reporting period.	0	0
Level 3 | Funds Withheld Receivable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	100,000,000	0
Realized and unrealized gains (losses), included in Net income (loss) as:
Investment gains (losses), reported in net investment income	0	0
Net derivative gains (losses)	0	0
Total realized and unrealized gains (losses)	0	0
Other comprehensive income (loss)	0	0
Purchases	0	0
Sales	0	0
Change in fair value of funds withheld assets	(129,000,000)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Closing Balance	(29,000,000)	0
Change in unrealized gains or losses for the period included in earnings for instruments held at the end of the reporting period	0	0
Change in unrealized gains or losses for the period included in other comprehensive income for instruments held at the end of the reporting period.	0	0
Level 3 | Modco Receivable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(411,000,000)	0
Realized and unrealized gains (losses), included in Net income (loss) as:
Investment gains (losses), reported in net investment income	0	0
Net derivative gains (losses)	0	0
Total realized and unrealized gains (losses)	0	0
Other comprehensive income (loss)	0	0
Purchases	0	0
Sales	0	0
Change in fair value of funds withheld assets	119,000,000
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Closing Balance	(292,000,000)	0
Change in unrealized gains or losses for the period included in earnings for instruments held at the end of the reporting period	0	0
Change in unrealized gains or losses for the period included in other comprehensive income for instruments held at the end of the reporting period.	$ 0	$ 0