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Investments (Portion Of Unrealized Gains And Losses On Equity Investments Held) (Detail) - Equity Securities [Member] - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Gains (losses) on equity investments [Member] |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |
Realized investment gains (losses) | $ 3 | $ 8 | $ 5 | $ (5)
Gains (losses) on equity investments sold during the period [Member] |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |
Realized investment gains (losses) | 0 | 0 | 0 | 0
Gains (losses) on equity investments still held at the end of the period [Member] |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |
Realized investment gains (losses) | $ 3 | $ 8 | $ 5 | $ (5)

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- Definition Amount of realized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3(a)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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