OTHER COMPREHENSIVE INCOME (LOSS) - Schedule of Reclassification from Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net gains (losses) on investments	$ (8)	$ 22
Income tax expense (benefit)	99	49
Other underwriting expenses	146	139
Net income (loss)	408	220
URA(D) on securities | Reclassification from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net gains (losses) on investments	4	11
Income tax expense (benefit)	(1)	(2)
Net income (loss)	3	9
Benefit plan net gain (loss) | Reclassification from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	0	0
Other underwriting expenses	1	0
Net income (loss)	$ 0	$ 0