Investments (Current And Long-Term Investments, Available-For-Sale) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	$ 720	$ 173
Fixed Maturity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	19,508	17,380
Gross Unrealized Gains	720	173
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(24)	(184)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(23)	(190)
Estimated Fair Value	20,181	17,179
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	524	414
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(1)
Estimated Fair Value	525	416
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	136	108
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	5	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(1)
Estimated Fair Value	141	108
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturity Securities [Member] \| States, Municipalities And Political Subdivisions, Tax-Exempt [Member]
Investment [Line Items]
Cost or Amortized Cost	4,592	4,716
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	262	91
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3)	(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(19)
Estimated Fair Value	4,851	4,785
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	8,870	8,189
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	339	33
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(9)	(170)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(15)	(115)
Estimated Fair Value	9,185	7,937
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(3)	(3)
Fixed Maturity Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	3,654	2,769
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	87	31
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(6)	(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(3)	(47)
Estimated Fair Value	3,732	2,750
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturity Securities [Member] \| Commercial Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	84	69
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(2)
Estimated Fair Value	86	67
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	1,648	1,115
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	21	14
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3)	(8)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5)	(5)
Estimated Fair Value	1,661	1,116
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	$ 0	$ 0

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