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Investments (Current And Long-Term Fixed Maturity Securities, Available-For-Sale) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Mar. 31, 2020	Jun. 30, 2019
Investments [Line Items]
Gross Unrealized Gains	$ 974			$ 626
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	24	$ 0	$ 51
Foreign Government Securities [Member]
Investments [Line Items]
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	1	0	0
Corporate Securities [Member]
Investments [Line Items]
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	23	0	$ 51
Fixed Maturities [Member]
Investments [Line Items]
Cost or Amortized Cost	21,849	19,508
Gross Unrealized Gains	974	720
Gross Unrealized Losses, Less than 12 Months	(209)	(24)
Gross Unrealized Losses, 12 Months or Greater	(52)	(23)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(24)	0
Available-for-sale Securities	22,538	20,181
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(32)	(3)
Fixed Maturities [Member] \| United States Government Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	1,250	524
Gross Unrealized Gains	17	4
Gross Unrealized Losses, Less than 12 Months	(1)	(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	1,266	525
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturities [Member] \| Government Sponsored Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	96	136
Gross Unrealized Gains	7	5
Gross Unrealized Losses, Less than 12 Months	(1)	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	102	141
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturities [Member] \| Foreign Government Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	288
Gross Unrealized Gains	7
Gross Unrealized Losses, Less than 12 Months	(15)
Gross Unrealized Losses, 12 Months or Greater	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(1)
Available-for-sale Securities	279
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0
Fixed Maturities [Member] \| States, Municipalities And Political Subdivisions [Member]
Investments [Line Items]
Cost or Amortized Cost	4,840	4,592
Gross Unrealized Gains	315	262
Gross Unrealized Losses, Less than 12 Months	(5)	(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	5,150	4,851
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturities [Member] \| Corporate Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	9,855	8,870
Gross Unrealized Gains	469	339
Gross Unrealized Losses, Less than 12 Months	(125)	(9)
Gross Unrealized Losses, 12 Months or Greater	(28)	(15)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(23)	0
Available-for-sale Securities	10,148	9,185
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(32)	(3)
Fixed Maturities [Member] \| Residential Mortgage-Backed Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	3,696	3,654
Gross Unrealized Gains	137	87
Gross Unrealized Losses, Less than 12 Months	(26)	(6)
Gross Unrealized Losses, 12 Months or Greater	(11)	(3)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	3,796	3,732
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturities [Member] \| Commercial Mortgage-Backed Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	80	84
Gross Unrealized Gains	2	2
Gross Unrealized Losses, Less than 12 Months	(2)	0
Gross Unrealized Losses, 12 Months or Greater	(4)	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	76	86
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturities [Member] \| Other Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	1,744	1,648
Gross Unrealized Gains	20	21
Gross Unrealized Losses, Less than 12 Months	(34)	(3)
Gross Unrealized Losses, 12 Months or Greater	(9)	(5)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	1,721	1,661
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	$ 0	$ 0