Investments (Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time) (Details) - Available-for-sale Securities - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
AFS Fair Value, Less than 12 Months	$ 5,693,945	$ 1,376,128
AFS Unrealized Losses, Less than 12 months	(514,307)	(14,849)
AFS Fair Value, 12 months or longer	444,242	85,122
AFS Unrealized Losses, 12 months or longer	(72,234)	(2,505)
AFS Fair Value	6,138,187	1,461,250
AFS Unrealized Losses	(586,541)	(17,354)
U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 Months	138,136	34,857
AFS Unrealized Losses, Less than 12 months	(16,003)	(746)
AFS Fair Value, 12 months or longer	9,819	7,827
AFS Unrealized Losses, 12 months or longer	(4,112)	(399)
AFS Fair Value	147,955	42,684
AFS Unrealized Losses	(20,115)	(1,145)
Foreign Government [Member]
AFS Fair Value, Less than 12 Months	12,069	2,000
AFS Unrealized Losses, Less than 12 months	(1,501)	(84)
AFS Fair Value, 12 months or longer	1,711	1,061
AFS Unrealized Losses, 12 months or longer	(459)	(39)
AFS Fair Value	13,780	3,061
AFS Unrealized Losses	(1,960)	(123)
Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 Months	921,980	25,837
AFS Unrealized Losses, Less than 12 months	(62,494)	(235)
AFS Fair Value, 12 months or longer	3,886	0
AFS Unrealized Losses, 12 months or longer	(643)	0
AFS Fair Value	925,866	25,837
AFS Unrealized Losses	(63,137)	(235)
Corporate Securities [Member]
AFS Fair Value, Less than 12 Months	2,037,738	300,549
AFS Unrealized Losses, Less than 12 months	(217,328)	(4,903)
AFS Fair Value, 12 months or longer	61,315	2,520
AFS Unrealized Losses, 12 months or longer	(17,655)	(50)
AFS Fair Value	2,099,053	303,069
AFS Unrealized Losses	(234,983)	(4,953)
Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months	1,107,292	663,976
AFS Unrealized Losses, Less than 12 months	(82,751)	(4,934)
AFS Fair Value, 12 months or longer	269,902	53,368
AFS Unrealized Losses, 12 months or longer	(29,541)	(1,350)
AFS Fair Value	1,377,194	717,344
AFS Unrealized Losses	(112,292)	(6,284)
Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	937,823	236,010
AFS Unrealized Losses, Less than 12 months	(93,871)	(2,931)
AFS Fair Value, 12 months or longer	45,296	20
AFS Unrealized Losses, 12 months or longer	(10,985)	(1)
AFS Fair Value	983,119	236,030
AFS Unrealized Losses	(104,856)	(2,932)
Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	538,907	112,899
AFS Unrealized Losses, Less than 12 months	(40,359)	(1,016)
AFS Fair Value, 12 months or longer	52,313	20,326
AFS Unrealized Losses, 12 months or longer	(8,839)	(666)
AFS Fair Value	591,220	133,225
AFS Unrealized Losses	$ (49,198)	$ (1,682)

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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