Investments (Summary Of Unrealized Appreciation (Depreciation) Of Available For Sale, Fixed Maturity And Equity Security Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 16,473,491
Unrealized Appreciation	472,622
Unrealized Depreciation	(121,169)
OTTI in AOCI	987
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,473,491	$ 15,406,572
Unrealized Appreciation	472,622	186,589
Unrealized Depreciation	(121,169)	(367,898)
Market Value	16,824,944	15,225,263
OTTI in AOCI	987	2,545
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,489,660	2,629,454
Unrealized Appreciation	28,357	16,781
Unrealized Depreciation	(2,214)	(15,101)
Market Value	1,515,803	2,631,134
OTTI in AOCI
Obligations Of U.S. States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	507,353	490,018
Unrealized Appreciation	29,651	12,915
Unrealized Depreciation	(89)	(2,839)
Market Value	536,915	500,094
OTTI in AOCI		439
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,227,661	5,538,582
Unrealized Appreciation	185,052	48,465
Unrealized Depreciation	(37,767)	(141,515)
Market Value	6,374,946	5,445,532
OTTI in AOCI	469	1,688
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	892,373	545,427
Unrealized Appreciation	6,818	162
Unrealized Depreciation	(1,858)	(5,492)
Market Value	897,333	540,097
OTTI in AOCI
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	814,570	329,883
Unrealized Appreciation	31,236	2,167
Unrealized Depreciation	(1,249)	(5,340)
Market Value	844,557	326,710
OTTI in AOCI
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,173,099	1,832,760
Unrealized Appreciation	36,361	7,325
Unrealized Depreciation	(10,879)	(43,821)
Market Value	2,198,581	1,796,264
OTTI in AOCI
Non-Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,723	10,198
Unrealized Appreciation		37
Unrealized Depreciation	(20)	(26)
Market Value	5,703	10,209
OTTI in AOCI
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,492,315	1,335,328
Unrealized Appreciation	47,148	34,743
Unrealized Depreciation	(33,513)	(55,906)
Market Value	1,505,950	1,314,165
OTTI in AOCI	71	98
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,870,737	2,694,922
Unrealized Appreciation	107,999	63,994
Unrealized Depreciation	(33,580)	(97,858)
Market Value	2,945,156	2,661,058
OTTI in AOCI	$ 447	$ 320

Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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