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Investments (Schedule Of Amortized Cost And Fair Value Of Held-to-Maturity And Related Other-Than-Temporary Impairment Recognized In Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | $ 11,697 | $ 12,581
Debt Securities, Held-to-maturity, Allowance for Credit Loss | 44 | 0
Debt securities, held to maturity, net carrying value | 11,653 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 859 | 427
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | (2) | (3)
Held to maturity, Fair Value | 12,510 | 13,005
Held to maturity, OTTI recognized in AOCI |  | 0
U.S. Treasury and agency |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 1,392 | 1,318
Debt Securities, Held-to-maturity, Allowance for Credit Loss | 0 |
Debt securities, held to maturity, net carrying value | 1,392 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 60 | 29
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | 0 | 0
Held to maturity, Fair Value | 1,452 | 1,347
Held to maturity, OTTI recognized in AOCI |  | 0
Foreign |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 1,295 | 1,423
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (7) |
Debt securities, held to maturity, net carrying value | 1,288 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 118 | 62
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | (1) | 0
Held to maturity, Fair Value | 1,405 | 1,485
Held to maturity, OTTI recognized in AOCI |  | 0
Corporate securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 2,185 | 2,349
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (35) |
Debt securities, held to maturity, net carrying value | 2,150 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 288 | 121
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | 0 | (2)
Held to maturity, Fair Value | 2,438 | 2,468
Held to maturity, OTTI recognized in AOCI |  | 0
Mortgage-backed securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 2,000 | 2,331
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (1) |
Debt securities, held to maturity, net carrying value | 1,999 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 148 | 65
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | (1) | 0
Held to maturity, Fair Value | 2,146 | 2,396
Held to maturity, OTTI recognized in AOCI |  | 0
States, municipalities, and political subdivisions |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 4,825 | 5,160
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (1) |
Debt securities, held to maturity, net carrying value | 4,824 |
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 245 | 150
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | 0 | (1)
Held to maturity, Fair Value | $ 5,069 | 5,309
Held to maturity, OTTI recognized in AOCI |  | $ 0

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- Definition Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as held-to-maturity that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 9A -URI http://asc.fasb.org/extlink&oid=121553693&loc=SL6284427-111562 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (dd) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 + Details
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- Definition Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aaa) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
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