FAIR VALUE OF ASSETS AND LIABILITIES - Changes in Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
U.S. corporate private securities \| Retained Business \| Fixed Maturity, Available-For Sale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	$ 244	$ 146	$ 146
Total realized and unrealized gains (losses)	3	0
Purchases	24	19
Sales	0	0
Issuances	0	0
Settlements	0	(1)
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	18
Fair Value, end of period	271	182	244
Unrealized gains (losses) for assets still held	2	0
U.S. corporate private securities \| Ceded Business \| Fixed Maturity, Available-For Sale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	1
Total realized and unrealized gains (losses)	0
Purchases	0
Sales	0
Issuances	0
Settlements	0
Other	0
Transfers into Level 3	0
Transfers out of Level 3	0
Fair Value, end of period	1		1
Unrealized gains (losses) for assets still held	0
Foreign corporate private securities \| Retained Business \| Fixed Maturity, Available-For Sale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	56	36	36
Total realized and unrealized gains (losses)	1	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	57	36	56
Unrealized gains (losses) for assets still held	1	1
Foreign corporate private securities \| Ceded Business
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	1
Total realized and unrealized gains (losses)	0
Purchases	0
Sales	0
Issuances	0
Settlements	(1)
Other	0
Transfers into Level 3	0
Transfers out of Level 3	0
Fair Value, end of period	0		1
Unrealized gains (losses) for assets still held	0
Residential mortgage-backed securities \| Retained Business \| Fixed Maturity, Available-For Sale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	5
Total realized and unrealized gains (losses)	0
Purchases	0
Sales	0
Issuances	0
Settlements	0
Other	0
Transfers into Level 3	0
Transfers out of Level 3	0
Fair Value, end of period	5		5
Unrealized gains (losses) for assets still held	0
Asset-backed securities \| Retained Business \| Fixed Maturity, Available-For Sale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	246	155	155
Total realized and unrealized gains (losses)	(1)	(2)
Purchases	14	38
Sales	0	0
Issuances	0	0
Settlements	(1)	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	258	191	246
Unrealized gains (losses) for assets still held	(2)	(2)
Asset-backed securities \| Ceded Business \| Fixed Maturity, Available-For Sale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	0
Total realized and unrealized gains (losses)	0
Purchases	28
Sales	0
Issuances	0
Settlements	0
Other	0
Transfers into Level 3	0
Transfers out of Level 3	0
Fair Value, end of period	28		0
Unrealized gains (losses) for assets still held	0
Short term investments \| Ceded Business
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	4
Total realized and unrealized gains (losses)	0
Purchases	3
Sales	0
Issuances	0
Settlements	(7)
Other	0
Transfers into Level 3	0
Transfers out of Level 3	0
Fair Value, end of period	0		4
Unrealized gains (losses) for assets still held	0
Residential mortgage loans \| Retained Business \| Equity securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	361	161	161
Total realized and unrealized gains (losses)	5	0
Purchases	4	13
Sales	0	0
Issuances	0	0
Settlements	(22)	(16)
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	348	158	361
Unrealized gains (losses) for assets still held	5	0
Commercial mortgage-backed securities \| Retained Business \| Equity securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	76	35	35
Total realized and unrealized gains (losses)	1	0
Purchases	0	13
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	77	48	76
Unrealized gains (losses) for assets still held	1	0
Deposit asset \| Ceded Business
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	438	607	607
Total realized and unrealized gains (losses)	(10)	1
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	(2)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	426	608	438
Unrealized gains (losses) for assets still held	0	0
Reinsurance recoverables \| Ceded Business
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	206	235	235
Total realized and unrealized gains (losses)	(51)	12
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	155	247	206
Unrealized gains (losses) for assets still held	0	0
Net modified coinsurance receivable (payable) \| Ceded Business
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, beginning of period	(78)	18	18
Total realized and unrealized gains (losses)	6	(63)
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair Value, end of period	(72)	(45)	$ (78)
Unrealized gains (losses) for assets still held	$ 0	$ 0

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Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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