Investments (Summary Of Amortized Cost And Market Value Of Fixed Maturity Securities, By Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	$ 16,392,238	$ 16,473,491
Fixed maturity securities - available for sale, Market Value	17,055,259	16,824,944
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	1,401,446	1,456,960
Fixed maturity securities - available for sale, Due after one year through five years, Amortized Cost	6,415,691	6,757,107
Fixed maturity securities - available for sale, Due after five years through ten years, Amortized Cost	3,712,330	3,471,370
Fixed maturity securities - available for sale, Due after ten years, Amortized Cost	915,873	902,289
Fixed maturity securities - available for sale, Due in one year or less, Market Value	1,413,299	1,457,919
Fixed maturity securities - available for sale, Due after one year through five years, Market Value	6,636,170	6,869,359
Fixed maturity securities - available for sale, Due after five years through ten years, Market Value	3,987,207	3,609,816
Fixed maturity securities - available for sale, Due after ten years, Market Value	936,867	941,676
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	1,076,648	892,373
Fixed maturity securities - available for sale, Market Value	1,069,558	897,333
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	850,616	814,570
Fixed maturity securities - available for sale, Market Value	919,796	844,557
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	2,016,481	2,173,099
Fixed maturity securities - available for sale, Market Value	2,089,251	2,198,581
Non-Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	3,153	5,723
Fixed maturity securities - available for sale, Market Value	$ 3,111	$ 5,703

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

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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