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INVESTMENTS - Summary of Amortized Cost and Fair Values of Fixed Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Available for sale
Amortized cost	$ 12,176,473	$ 12,241,782
Allowance for expected credit losses	(11,733)	(313)	$ (323)	$ 0
Gross unrealized gains	18,742	165,977
Gross unrealized losses	(856,588)	(94,246)
Fair value	11,326,894	12,313,200
U.S. government and agency
Available for sale
Amortized cost	2,731,733	2,693,319
Allowance for expected credit losses	0	0
Gross unrealized gains	5,386	9,776
Gross unrealized losses	(97,789)	(20,647)
Fair value	2,639,330	2,682,448
Non-U.S. government
Available for sale
Amortized cost	612,546	794,705
Allowance for expected credit losses	0	0
Gross unrealized gains	2,395	10,158
Gross unrealized losses	(52,912)	(9,685)
Fair value	562,029	795,178
Corporate debt
Available for sale
Amortized cost	4,680,798	4,446,585
Allowance for expected credit losses	(11,521)	(236)
Gross unrealized gains	5,269	87,075
Gross unrealized losses	(418,990)	(38,112)
Fair value	4,255,556	4,495,312
Agency RMBS
Available for sale
Amortized cost	1,297,423	1,065,973
Allowance for expected credit losses	0	0
Gross unrealized gains	4,663	17,397
Gross unrealized losses	(99,301)	(8,781)
Fair value	1,202,785	1,074,589
CMBS
Available for sale
Amortized cost	1,029,863	1,223,051
Allowance for expected credit losses	0	0
Gross unrealized gains	60	29,827
Gross unrealized losses	(82,145)	(4,687)
Fair value	947,778	1,248,191
Non-agency RMBS
Available for sale
Amortized cost	151,907	185,854
Allowance for expected credit losses	(123)	(77)
Gross unrealized gains	275	2,410
Gross unrealized losses	(18,525)	(2,023)
Fair value	133,534	186,164
ABS
Available for sale
Amortized cost	1,499,728	1,628,739
Allowance for expected credit losses	(35)	0
Gross unrealized gains	555	3,406
Gross unrealized losses	(70,721)	(9,665)
Fair value	1,429,527	1,622,480
Municipals
Available for sale
Amortized cost	172,475	203,556
Allowance for expected credit losses	(54)	0
Gross unrealized gains	139	5,928
Gross unrealized losses	(16,205)	(646)
Fair value	$ 156,355	$ 208,838