Investments (Current And Long-Term Investments, Available-For-Sale) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Investment [Line Items]
Gross Unrealized Gains	$ 1,316	$ 720
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	7	0
Fixed Maturity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	22,754	19,508
Gross Unrealized Gains	1,316	720
Gross unrealized loss, less than 12 Months	(39)	(24)
Gross unrealized loss, 12 Months or greater	(29)	(23)
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	7	0
Estimated Fair Value	23,995	20,181
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(3)	(3)
Fixed Maturity Securities [Member] \| United States Government Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	765	524
Gross Unrealized Gains	11	4
Gross unrealized loss, less than 12 Months	(2)	(3)
Gross unrealized loss, 12 Months or greater	0	0
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	0	0
Estimated Fair Value	774	525
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturity Securities [Member] \| Government Sponsored Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	63	136
Gross Unrealized Gains	6	5
Gross unrealized loss, less than 12 Months	0	0
Gross unrealized loss, 12 Months or greater	0	0
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	0	0
Estimated Fair Value	69	141
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturity Securities [Member] \| Foreign Government Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	290
Gross Unrealized Gains	17
Gross unrealized loss, less than 12 Months	(2)
Gross unrealized loss, 12 Months or greater	0
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	0	0
Estimated Fair Value	305
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0
Fixed Maturity Securities [Member] \| States, Municipalities And Political Subdivisions, Tax-Exempt [Member]
Investment [Line Items]
Cost or Amortized Cost	5,185	4,592
Gross Unrealized Gains	395	262
Gross unrealized loss, less than 12 Months	(1)	(3)
Gross unrealized loss, 12 Months or greater	0	0
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	0	0
Estimated Fair Value	5,579	4,851
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturity Securities [Member] \| Corporate Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	10,233	8,870
Gross Unrealized Gains	697	339
Gross unrealized loss, less than 12 Months	(20)	(9)
Gross unrealized loss, 12 Months or greater	(11)	(15)
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	7	0
Estimated Fair Value	10,892	9,185
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(1)	(3)
Fixed Maturity Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	4,208	3,654
Gross Unrealized Gains	154	87
Gross unrealized loss, less than 12 Months	(8)	(6)
Gross unrealized loss, 12 Months or greater	(9)	(3)
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	0	0
Estimated Fair Value	4,345	3,732
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(2)	0
Fixed Maturity Securities [Member] \| Commercial Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	73	84
Gross Unrealized Gains	3	2
Gross unrealized loss, less than 12 Months	(1)	0
Gross unrealized loss, 12 Months or greater	(3)	0
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	0	0
Estimated Fair Value	72	86
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturity Securities [Member] \| Other Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	1,937	1,648
Gross Unrealized Gains	33	21
Gross unrealized loss, less than 12 Months	(5)	(3)
Gross unrealized loss, 12 Months or greater	(6)	(5)
Fixed maturity securities, Available-for-sale, Allowance for Credit Loss	0	0
Estimated Fair Value	1,959	1,661
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	$ 0	$ 0

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