SEGMENT REPORTING - Schedule of Underwriting Results for Operating Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Gross written premiums	$ 2,772	$ 2,496
Net written premiums	2,266	2,063
Premiums earned	2,231	2,068
Incurred losses and LAE	1,375	1,394
Commission and brokerage	472	436
Other underwriting expenses	146	139
Underwriting gain (loss)	237	99
Net investment income	312	190
Net gains (losses) on investments	(8)	22
Corporate expenses	(5)	(6)
Interest, fees and bond issue cost amortization expense	(37)	(32)
Other income (expense)	7	(4)
INCOME (LOSS) BEFORE TAXES	507	269
Reinsurance
Segment Reporting Information [Line Items]
Gross written premiums	1,935	1,627
Net written premiums	1,624	1,357
Premiums earned	1,558	1,351
Incurred losses and LAE	932	919
Commission and brokerage	402	357
Other underwriting expenses	46	38
Underwriting gain (loss)	178	36
Insurance
Segment Reporting Information [Line Items]
Gross written premiums	837	869
Net written premiums	642	706
Premiums earned	672	718
Incurred losses and LAE	443	475
Commission and brokerage	70	80
Other underwriting expenses	100	101
Underwriting gain (loss)	$ 59	$ 63