Investments (Summary Of Unrealized Appreciation (Depreciation) Of Available For Sale, Fixed Maturity And Equity Security Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 22,693,029	$ 22,063,592
Allowance for credit losses	(41,591)	(29,738)	$ (8,723)	$ (1,745)
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,693,029	22,063,592
Allowance for credit losses	(41,591)	(29,738)
Unrealized Appreciation	153,729	477,548
Unrealized Depreciation	(806,752)	(203,130)
Market Value	21,998,415	22,308,272
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,387,723	1,407,256
Allowance for credit losses
Unrealized Appreciation	9,506	23,720
Unrealized Depreciation	(41,423)	(10,358)
Market Value	1,355,806	1,420,618
Obligations Of U.S. States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	560,375	558,842
Allowance for credit losses	(151)	(151)
Unrealized Appreciation	9,538	29,080
Unrealized Depreciation	(10,574)	(1,150)
Market Value	559,188	586,621
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,510,255	7,443,535
Allowance for credit losses	(20,049)	(19,267)	(3,603)	(1,220)
Unrealized Appreciation	64,802	195,210
Unrealized Depreciation	(263,958)	(62,580)
Market Value	7,291,050	7,556,898
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,046,636	3,579,439
Allowance for credit losses	(7,679)	(7,679)	(4,915)
Unrealized Appreciation	13,228	21,817
Unrealized Depreciation	(54,294)	(11,848)
Market Value	3,997,891	3,581,729
Mortgage-Backed Securities: Commercial [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,021,013	1,032,506
Allowance for credit losses
Unrealized Appreciation	2,762	37,550
Unrealized Depreciation	(31,904)	(5,690)
Market Value	991,871	1,064,366
Mortgage Backed Securities: Agency residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,387,754	2,361,208
Allowance for credit losses
Unrealized Appreciation	5,354	32,997
Unrealized Depreciation	(109,611)	(18,873)
Market Value	2,283,497	2,375,332
Mortgage Backed Securities: Non-agency residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,759	6,530
Allowance for credit losses
Unrealized Appreciation		22
Unrealized Depreciation	(114)	(16)
Market Value	5,645	6,536
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,414,589	1,423,634
Allowance for credit losses				(22)
Unrealized Appreciation	16,763	41,957
Unrealized Depreciation	(68,970)	(28,079)
Market Value	1,362,382	1,437,512
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,358,925	4,250,642
Allowance for credit losses	(13,712)	(2,641)	$ (205)	$ (503)
Unrealized Appreciation	31,776	95,195
Unrealized Depreciation	(225,904)	(64,536)
Market Value	$ 4,151,085	$ 4,278,660