Fair Value (Reconciliation Of The Beginning And Ending Balances Of Assets Measured At Fair Value On A Recurring Basis Using Level III Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 397	$ 623	$ 537
Gains (losses) recognized in net income	(22)	(13)	(228)
Gains (losses) recognized in accumulated other comprehensive loss/income	(5)	3	(5)
Purchases	101	189	430
Sales	(41)	(101)	(69)
Settlements	(46)	(79)	(99)
Transfers into Level III	10	5	74
Transfers out of Level III	(2)	(230)	(17)
Ending balance	392	397	623
Change in unrealized losses included in net income related to assets still held	(19)	6	30
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	303	287	229
Gains (losses) recognized in net income	(3)	(7)	1
Gains (losses) recognized in accumulated other comprehensive loss/income	(5)	3	(5)
Purchases	85	122	120
Sales	(19)	(22)	(33)
Settlements	(44)	(71)	(88)
Transfers into Level III	10	0	65
Transfers out of Level III	(2)	(9)	(2)
Ending balance	325	303	287
Change in unrealized losses included in net income related to assets still held	0	0	0
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	2	6	5
Gains (losses) recognized in net income	0	0	0
Gains (losses) recognized in accumulated other comprehensive loss/income	0	0	0
Purchases	0	0	2
Sales	0	0	0
Settlements	0	(2)	(1)
Transfers into Level III	0	0	0
Transfers out of Level III	0	(2)	0
Ending balance	2	2	6
Change in unrealized losses included in net income related to assets still held	0	0	0
Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	7	17	16
Gains (losses) recognized in net income	0	0	0
Gains (losses) recognized in accumulated other comprehensive loss/income	0	0	0
Purchases	0	2	18
Sales	0	0	(1)
Settlements	(2)	(6)	(10)
Transfers into Level III	0	3	9
Transfers out of Level III	0	(9)	(15)
Ending balance	5	7	17
Change in unrealized losses included in net income related to assets still held	0	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	85	313	287
Gains (losses) recognized in net income	(19)	(6)	(229)
Gains (losses) recognized in accumulated other comprehensive loss/income	0	0	0
Purchases	16	65	290
Sales	(22)	(79)	(35)
Settlements	0	0	0
Transfers into Level III	0	2	0
Transfers out of Level III	0	(210)	0
Ending balance	60	85	313
Change in unrealized losses included in net income related to assets still held	$ (19)	$ 6	$ 30

Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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