INVESTMENTS - Gross Unrealized Losses (Details) $ in Thousands	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Fixed maturities, available for sale
Fair value
12 months or greater	$ 6,555,825	$ 3,615,234
Less than 12 months	4,629,740	6,269,478
Total	11,185,565	9,884,712
Unrealized losses
12 months or greater	(705,729)	(497,762)
Less than 12 months	(156,961)	(358,826)
Total	$ (862,690)	$ (856,588)
Number of securities in unrealized loss position | security	4,856	4,525
Number of securities in a continuous unrealized loss position | security	3,386	1,842
Fixed maturities, available for sale | Below Investment Grade or Not Rated
Unrealized losses
Total	$ (39,000)	$ (64,000)
U.S. government and agency
Fair value
12 months or greater	933,401	467,032
Less than 12 months	1,841,396	1,414,181
Total	2,774,797	1,881,213
Unrealized losses
12 months or greater	(68,216)	(41,365)
Less than 12 months	(47,816)	(56,424)
Total	(116,032)	(97,789)
Non-U.S. government
Fair value
12 months or greater	236,921	207,637
Less than 12 months	400,356	298,048
Total	637,277	505,685
Unrealized losses
12 months or greater	(31,958)	(33,027)
Less than 12 months	(16,922)	(19,885)
Total	(48,880)	(52,912)
Corporate debt
Fair value
12 months or greater	2,705,183	1,562,355
Less than 12 months	1,207,859	2,350,504
Total	3,913,042	3,912,859
Unrealized losses
12 months or greater	(333,349)	(268,289)
Less than 12 months	(44,020)	(150,701)
Total	(377,369)	(418,990)
Agency RMBS
Fair value
12 months or greater	751,020	220,595
Less than 12 months	783,310	771,191
Total	1,534,330	991,786
Unrealized losses
12 months or greater	(128,711)	(40,469)
Less than 12 months	(37,431)	(58,832)
Total	(166,142)	(99,301)
CMBS
Fair value
12 months or greater	732,637	343,494
Less than 12 months	121,722	599,877
Total	854,359	943,371
Unrealized losses
12 months or greater	(75,522)	(40,888)
Less than 12 months	(6,833)	(41,257)
Total	(82,355)	(82,145)
Non-agency RMBS
Fair value
12 months or greater	92,894	75,137
Less than 12 months	37,539	53,484
Total	130,433	128,621
Unrealized losses
12 months or greater	(16,856)	(14,691)
Less than 12 months	(767)	(3,834)
Total	(17,623)	(18,525)
ABS
Fair value
12 months or greater	975,560	685,990
Less than 12 months	216,048	686,190
Total	1,191,608	1,372,180
Unrealized losses
12 months or greater	(36,001)	(48,913)
Less than 12 months	(2,448)	(21,808)
Total	(38,449)	(70,721)
Municipals
Fair value
12 months or greater	128,209	52,994
Less than 12 months	21,510	96,003
Total	149,719	148,997
Unrealized losses
12 months or greater	(15,116)	(10,120)
Less than 12 months	(724)	(6,085)
Total	$ (15,840)	$ (16,205)