INVESTMENTS - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Debt Securities, Available-for-Sale [Line Items]
Fair value of investments in unrealized loss position	$ 7,930	$ 7,556
Gross unrealized losses on investments in unrealized loss position	550	536
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	51	55
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	499	481
Additional contractual commitments	1,000
Cash surrender value of life insurance	$ 1,400	$ 1,300
Number of securities held as primary beneficiary | security	0	0
Variable Interest Entity, Not Primary Beneficiary
Debt Securities, Available-for-Sale [Line Items]
Maximum exposure to loss	$ 3,300	$ 3,300
Commitments to fund investments	$ 980
Investments, Debt Securities Benchmark | Issuer Concentration Risk | Issuer One
Debt Securities, Available-for-Sale [Line Items]
Percentage of overall fair value of fixed maturity securities available for sale, less than	1.40%	1.40%
Investments, Debt Securities Benchmark | Issuer Concentration Risk | Issuer Two
Debt Securities, Available-for-Sale [Line Items]
Percentage of overall fair value of fixed maturity securities available for sale, less than	0.50%	0.50%
Investment Grade
Debt Securities, Available-for-Sale [Line Items]
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	$ 43	$ 39
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	475	455
Fixed maturities
Debt Securities, Available-for-Sale [Line Items]
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation		55
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	$ 499	$ 481