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Investments (Current And Long-Term Fixed Maturity Securities, Available-For-Sale) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Sep. 30, 2019
Investments [Line Items]
Gross Unrealized Gains	$ 1,136			$ 770
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	12	$ 0	$ 24
Foreign Government Securities [Member]
Investments [Line Items]
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	1	0	1
Corporate Securities [Member]
Investments [Line Items]
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	11	0	$ 23
Fixed Maturities [Member]
Investments [Line Items]
Cost or Amortized Cost	22,397	19,508
Gross Unrealized Gains	1,136	720
Gross Unrealized Losses, Less than 12 Months	(214)	(24)
Gross Unrealized Losses, 12 Months or Greater	(42)	(23)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(12)	0
Available-for-sale Securities	23,265	20,181
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	(11)	(3)
Fixed Maturities [Member] \| United States Government Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	802	524
Gross Unrealized Gains	17	4
Gross Unrealized Losses, Less than 12 Months	(6)	(3)
Gross Unrealized Losses, 12 Months or Greater	0	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	813	525
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	0	0
Fixed Maturities [Member] \| Government Sponsored Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	75	136
Gross Unrealized Gains	6	5
Gross Unrealized Losses, Less than 12 Months	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	81	141
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	0	0
Fixed Maturities [Member] \| Foreign Government Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	296
Gross Unrealized Gains	10
Gross Unrealized Losses, Less than 12 Months	(13)
Gross Unrealized Losses, 12 Months or Greater	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(1)
Available-for-sale Securities	292
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	0
Fixed Maturities [Member] \| States, Municipalities And Political Subdivisions [Member]
Investments [Line Items]
Cost or Amortized Cost	5,042	4,592
Gross Unrealized Gains	339	262
Gross Unrealized Losses, Less than 12 Months	(18)	(3)
Gross Unrealized Losses, 12 Months or Greater	0	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	5,363	4,851
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	0	0
Fixed Maturities [Member] \| Corporate Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	10,140	8,870
Gross Unrealized Gains	579	339
Gross Unrealized Losses, Less than 12 Months	(114)	(9)
Gross Unrealized Losses, 12 Months or Greater	(23)	(15)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(11)	0
Available-for-sale Securities	10,571	9,185
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	(10)	(3)
Fixed Maturities [Member] \| Residential Mortgage-Backed Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	4,075	3,654
Gross Unrealized Gains	151	87
Gross Unrealized Losses, Less than 12 Months	(48)	(6)
Gross Unrealized Losses, 12 Months or Greater	(10)	(3)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	4,168	3,732
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	(1)	0
Fixed Maturities [Member] \| Commercial Mortgage-Backed Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	76	84
Gross Unrealized Gains	3	2
Gross Unrealized Losses, Less than 12 Months	(1)	0
Gross Unrealized Losses, 12 Months or Greater	(3)	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	75	86
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	0	0
Fixed Maturities [Member] \| Other Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	1,891	1,648
Gross Unrealized Gains	31	21
Gross Unrealized Losses, Less than 12 Months	(14)	(3)
Gross Unrealized Losses, 12 Months or Greater	(6)	(5)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	1,902	1,661
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Loss	$ 0	$ 0