Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Available for sale securities:
Estimated Fair Value - Less than 12 Months	$ 12,975,400	$ 12,238,683
Gross Unrealized Losses - Less than 12 Months	(927,531)	(157,279)
Estimated Fair Value - 12 Months or More	5,671,580	297,357
Gross Unrealized Losses - 12 Months or More	(720,756)	(14,265)
Estimated Fair Value - Total	18,646,980	12,536,040
Gross Unrealized Losses - Total	(1,648,287)	(171,544)
Fixed maturities available for sale, at fair value
Available for sale securities:
Estimated Fair Value - Less than 12 Months	12,738,665	11,953,950
Gross Unrealized Losses - Less than 12 Months	(925,643)	(156,689)
Estimated Fair Value - 12 Months or More	5,671,580	297,357
Gross Unrealized Losses - 12 Months or More	(720,756)	(14,265)
Estimated Fair Value - Total	18,410,245	12,251,307
Gross Unrealized Losses - Total	(1,646,399)	(170,954)
Fixed maturities available for sale, at fair value \| Corporate bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	4,822,624	3,639,582
Gross Unrealized Losses - Less than 12 Months	(393,112)	(63,938)
Estimated Fair Value - 12 Months or More	2,559,399	98,867
Gross Unrealized Losses - 12 Months or More	(388,241)	(5,256)
Estimated Fair Value - Total	7,382,023	3,738,449
Gross Unrealized Losses - Total	(781,353)	(69,194)
Fixed maturities available for sale, at fair value \| Mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	545,844	222,176
Gross Unrealized Losses - Less than 12 Months	(51,673)	(3,545)
Estimated Fair Value - 12 Months or More	154,154	46,809
Gross Unrealized Losses - 12 Months or More	(34,914)	(1,865)
Estimated Fair Value - Total	699,998	268,985
Gross Unrealized Losses - Total	(86,587)	(5,410)
Fixed maturities available for sale, at fair value \| Municipal bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	363,936	26,665
Gross Unrealized Losses - Less than 12 Months	(29,924)	(385)
Estimated Fair Value - 12 Months or More	16,282	16,361
Gross Unrealized Losses - 12 Months or More	(3,436)	(1,024)
Estimated Fair Value - Total	380,218	43,026
Gross Unrealized Losses - Total	(33,360)	(1,409)
Fixed maturities available for sale, at fair value \| Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	598,392	675,603
Gross Unrealized Losses - Less than 12 Months	(34,899)	(2,805)
Estimated Fair Value - 12 Months or More	445,175	5,908
Gross Unrealized Losses - 12 Months or More	(22,768)	(312)
Estimated Fair Value - Total	1,043,567	681,511
Gross Unrealized Losses - Total	(57,667)	(3,117)
Fixed maturities available for sale, at fair value \| US government and government agencies
Available for sale securities:
Estimated Fair Value - Less than 12 Months	3,556,676	4,211,621
Gross Unrealized Losses - Less than 12 Months	(197,259)	(44,180)
Estimated Fair Value - 12 Months or More	1,442,542	33,373
Gross Unrealized Losses - 12 Months or More	(145,704)	(1,787)
Estimated Fair Value - Total	4,999,218	4,244,994
Gross Unrealized Losses - Total	(342,963)	(45,967)
Fixed maturities available for sale, at fair value \| Non-US government securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	1,702,973	1,511,301
Gross Unrealized Losses - Less than 12 Months	(153,587)	(31,983)
Estimated Fair Value - 12 Months or More	541,652	62,957
Gross Unrealized Losses - 12 Months or More	(84,259)	(2,766)
Estimated Fair Value - Total	2,244,625	1,574,258
Gross Unrealized Losses - Total	(237,846)	(34,749)
Fixed maturities available for sale, at fair value \| Asset backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	1,148,220	1,667,002
Gross Unrealized Losses - Less than 12 Months	(65,189)	(9,853)
Estimated Fair Value - 12 Months or More	512,376	33,082
Gross Unrealized Losses - 12 Months or More	(41,434)	(1,255)
Estimated Fair Value - Total	1,660,596	1,700,084
Gross Unrealized Losses - Total	(106,623)	(11,108)
Short-term investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months	236,735	284,733
Gross Unrealized Losses - Less than 12 Months	(1,888)	(590)
Estimated Fair Value - 12 Months or More	0	0
Gross Unrealized Losses - 12 Months or More	0	0
Estimated Fair Value - Total	236,735	284,733
Gross Unrealized Losses - Total	$ (1,888)	$ (590)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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