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Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	$ 14,940,746	$ 12,238,683
Estimated Fair Value - 12 Months or More	2,936,029	297,357
Estimated Fair Value	17,876,775	12,536,040
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(1,376,623)	(157,279)
Gross Unrealized Losses - 12 Months or More	(485,664)	(14,265)
Gross Unrealized Losses	(1,862,287)	(171,544)
Fixed maturities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	14,713,545	11,953,950
Estimated Fair Value - 12 Months or More	2,936,029	297,357
Estimated Fair Value	17,649,574	12,251,307
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(1,374,990)	(156,689)
Gross Unrealized Losses - 12 Months or More	(485,664)	(14,265)
Gross Unrealized Losses	(1,860,654)	(170,954)
Corporate bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	5,596,229	3,639,582
Estimated Fair Value - 12 Months or More	1,470,800	98,867
Estimated Fair Value	7,067,029	3,738,449
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(625,774)	(63,938)
Gross Unrealized Losses - 12 Months or More	(269,591)	(5,256)
Gross Unrealized Losses	(895,365)	(69,194)
Mortgage backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	620,572	222,176
Estimated Fair Value - 12 Months or More	93,902	46,809
Estimated Fair Value	714,474	268,985
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(63,732)	(3,545)
Gross Unrealized Losses - 12 Months or More	(20,451)	(1,865)
Gross Unrealized Losses	(84,183)	(5,410)
Municipal bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	373,219	26,665
Estimated Fair Value - 12 Months or More	9,399	16,361
Estimated Fair Value	382,618	43,026
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(36,039)	(385)
Gross Unrealized Losses - 12 Months or More	(1,653)	(1,024)
Gross Unrealized Losses	(37,692)	(1,409)
Commercial mortgage backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	995,680	675,603
Estimated Fair Value - 12 Months or More	34,445	5,908
Estimated Fair Value	1,030,125	681,511
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(49,215)	(2,805)
Gross Unrealized Losses - 12 Months or More	(795)	(312)
Gross Unrealized Losses	(50,010)	(3,117)
US government and government agencies
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	4,205,475	4,211,621
Estimated Fair Value - 12 Months or More	715,347	33,373
Estimated Fair Value	4,920,822	4,244,994
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(303,805)	(44,180)
Gross Unrealized Losses - 12 Months or More	(96,979)	(1,787)
Gross Unrealized Losses	(400,784)	(45,967)
Non-US government securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	1,728,965	1,511,301
Estimated Fair Value - 12 Months or More	301,298	62,957
Estimated Fair Value	2,030,263	1,574,258
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(221,540)	(31,983)
Gross Unrealized Losses - 12 Months or More	(66,043)	(2,766)
Gross Unrealized Losses	(287,583)	(34,749)
Asset backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	1,193,405	1,667,002
Estimated Fair Value - 12 Months or More	310,838	33,082
Estimated Fair Value	1,504,243	1,700,084
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(74,885)	(9,853)
Gross Unrealized Losses - 12 Months or More	(30,152)	(1,255)
Gross Unrealized Losses	(105,037)	(11,108)
Short-term investments
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	227,201	284,733
Estimated Fair Value - 12 Months or More	0	0
Estimated Fair Value	227,201	284,733
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(1,633)	(590)
Gross Unrealized Losses - 12 Months or More	0	0
Gross Unrealized Losses	$ (1,633)	$ (590)

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