Investments (Current And Long-Term Fixed Maturity Securities, Available-For-Sale) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Investments [Line Items]
Gross Unrealized Gains	$ 510		$ 379
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	51	$ 0
Corporate Securities [Member]
Investments [Line Items]
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss		0
Fixed Maturities [Member]
Investments [Line Items]
Cost or Amortized Cost	20,700	19,508
Gross Unrealized Gains	510	720
Gross Unrealized Losses, Less than 12 Months	(707)	(24)
Gross Unrealized Losses, 12 Months or Greater	(66)	(23)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(51)	0
Available-for-sale Securities	20,386	20,181
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(44)	(3)
Fixed Maturities [Member] \| United States Government Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	450	524
Gross Unrealized Gains	24	4
Gross Unrealized Losses, Less than 12 Months	0	(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	474	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	369	136
Gross Unrealized Gains	5	5
Gross Unrealized Losses, Less than 12 Months	(48)	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	326	141
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0	0
Fixed Maturities [Member] \| States, Municipalities And Political Subdivisions [Member]
Investments [Line Items]
Cost or Amortized Cost	4,768	4,592
Gross Unrealized Gains	233	262
Gross Unrealized Losses, Less than 12 Months	(14)	(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	4,987	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	9,609	8,870
Gross Unrealized Gains	148	339
Gross Unrealized Losses, Less than 12 Months	(450)	(9)
Gross Unrealized Losses, 12 Months or Greater	(44)	(15)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	(51)	0
Available-for-sale Securities	9,212	9,185
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(44)	(3)
Fixed Maturities [Member] \| Residential Mortgage-Backed Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	3,731	3,654
Gross Unrealized Gains	93	87
Gross Unrealized Losses, Less than 12 Months	(95)	(6)
Gross Unrealized Losses, 12 Months or Greater	(7)	(3)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	3,722	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	81	84
Gross Unrealized Gains	1	2
Gross Unrealized Losses, Less than 12 Months	(3)	0
Gross Unrealized Losses, 12 Months or Greater	(1)	0
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	78	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	1,692	1,648
Gross Unrealized Gains	6	21
Gross Unrealized Losses, Less than 12 Months	(97)	(3)
Gross Unrealized Losses, 12 Months or Greater	(14)	(5)
Fixed Maturity Securities, Available-for-sale, Allowance for Credit Loss	0	0
Available-for-sale Securities	1,587	1,661
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	$ 0	$ 0

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount before tax of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss, attributable to parent entity.

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