OTHER COMPREHENSIVE INCOME (LOSS) - Reclassification From Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on investments	$ (22)	$ (378)	$ 0	$ (605)
Other underwriting expenses	136	120	275	238
Income tax expense (benefit)	81	(25)	130	(35)
Net income (loss)	330	(86)	549	(85)
URA(D) on securities | Reclassification From Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on investments	8	8	19	11
Income tax expense (benefit)	(2)	(2)	(4)	(2)
Net income (loss)	6	6	15	8
Benefit plan net gain (loss) | Reclassification From Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other underwriting expenses	1	1	1	2
Income tax expense (benefit)	0	0	0	0
Net income (loss)	$ 0	$ 1	$ 1	$ 2