Investments (Summary Of Amortized Cost And Market Value Of Fixed Maturity Securities, By Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 13,182,332	$ 12,733,499
Market Value	12,811,657	12,860,395
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Due in one year or less, Amortized Cost	531,594	586,432
Fixed maturity securities - available for sale, Due after one year through five years, Amortized Cost	3,581,700	3,488,358
Fixed maturity securities - available for sale, Due after five years through ten years, Amortized Cost	2,212,469	2,260,481
Fixed maturity securities - available for sale, Due after ten years, Amortized Cost	1,169,953	1,087,955
Amortized Cost	13,182,332	12,733,499
Fixed maturity securities - available for sale, Due in one year or less, Market Value	528,253	583,676
Fixed maturity securities - available for sale, Due after one year through five years, Market Value	3,492,586	3,526,854
Fixed maturity securities - available for sale, Due after five years through ten years, Market Value	2,120,957	2,309,870
Fixed maturity securities - available for sale, Due after ten years, Market Value	1,109,619	1,105,729
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,902,584	3,464,248
Market Value	3,856,965	3,466,286
Commercial [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	560,337	586,441
Market Value	542,934	602,894
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,219,867	1,255,186
Market Value	1,156,593	1,260,678
Non-agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,828	4,398
Market Value	$ 3,750	$ 4,408

Amount of debt securities categorized neither as held-to-maturity nor trading, held at market value.

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