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	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 383	$ 616	$ 397	$ 623
Total gains (losses) recognized in net income	(4)	(8)	(21)	(12)
Total gains (losses) recognized in accumulated other comprehensive loss	14	12	(3)	14
Purchases	7	53	61	139
Sales	(5)	(28)	(31)	(59)
Settlements	(14)	(18)	(35)	(61)
Transfers into Level III		4	13	7
Transfers out of Level III				(20)
Ending balance	381	631	381	631
Change in unrealized gains (losses) included in net income related to assets still held	(3)	(4)	(20)	(4)
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	314	297	303	287
Total gains (losses) recognized in net income	(1)	(3)	(2)	(7)
Total gains (losses) recognized in accumulated other comprehensive loss	14	12	(3)	14
Purchases	5	28	44	91
Sales	(5)	(9)	(9)	(11)
Settlements	(14)	(18)	(33)	(58)
Transfers into Level III		4	13	4
Transfers out of Level III				(9)
Ending balance	313	311	313	311
Change in unrealized gains (losses) included in net income related to assets still held	0	0	0	0
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	2	3	2	6
Total gains (losses) recognized in net income	0	0	0	0
Total gains (losses) recognized in accumulated other comprehensive loss	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	(1)
Transfers into Level III		0	0	0
Transfers out of Level III				(2)
Ending balance	2	3	2	3
Change in unrealized gains (losses) included in net income related to assets still held	0	0	0	0
Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5	11	7	17
Total gains (losses) recognized in net income	0	0	0	0
Total gains (losses) recognized in accumulated other comprehensive loss	0	0	0	0
Purchases	0	0	0	2
Sales	0	0	0	0
Settlements	0	0	(2)	(2)
Transfers into Level III		0	0	3
Transfers out of Level III				(9)
Ending balance	5	11	5	11
Change in unrealized gains (losses) included in net income related to assets still held	0	0	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	62	305	85	313
Total gains (losses) recognized in net income	(3)	(5)	(19)	(5)
Total gains (losses) recognized in accumulated other comprehensive loss	0	0	0	0
Purchases	2	25	17	46
Sales	0	(19)	(22)	(48)
Settlements	0	0	0	0
Transfers into Level III		0	0	0
Transfers out of Level III				0
Ending balance	61	306	61	306
Change in unrealized gains (losses) included in net income related to assets still held	$ (3)	$ (4)	$ (20)	$ (4)

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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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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- Definition

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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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.

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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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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

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-Publisher FASB
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-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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