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Investments (Fair Value Below Amortized Cost of Gross Unrealized Losses for Fixed Maturity and Equity Securities) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Gross unrealized losses with number of securities [Line Items] |  |
Available-for-sale Securities, Gross Unrealized Losses | $ 197 | $ 110
Percentage Of Total Gross Unrealized Losses | 100.00% | 100.00%
Less Than 20 Percent [Member] |  |
Gross unrealized losses with number of securities [Line Items] |  |
Available-for-sale Securities, Gross Unrealized Losses | $ 133 | $ 76
Percentage Of Total Gross Unrealized Losses | 67.50% | 69.10%
More Than Or Equal To 20 Percent For Less Than Six Months [Member] |  |
Gross unrealized losses with number of securities [Line Items] |  |
Available-for-sale Securities, Gross Unrealized Losses | $ 42 | $ 20
Percentage Of Total Gross Unrealized Losses | 21.30% | 18.20%
More Than Or Equal To 20 Percent For Six Months Or Greater [Member] |  |
Gross unrealized losses with number of securities [Line Items] |  |
Available-for-sale Securities, Gross Unrealized Losses | $ 22 | $ 14
Percentage Of Total Gross Unrealized Losses | 11.20% | 12.70%

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- Definition Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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