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Investments (Portion Of Unrealized Gains And Losses On Equity Investmente Held) (Detail) - Equity Securities [Member] - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2018
Gains (losses) on equity investments [Member] |  |
Gain (Loss) on Investments [Line Items] |  |
Realized investment gains (losses) | $ 0 | $ 0
Gains (losses) on equity investments sold during the period [Member] |  |
Gain (Loss) on Investments [Line Items] |  |
Realized investment gains (losses) | 1 | 1
Gains (losses) on equity investments still held at the end of the period [Member] |  |
Gain (Loss) on Investments [Line Items] |  |
Realized investment gains (losses) | $ (1) | $ (1)

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- Definition The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3(a)) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 325 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031664&loc=d3e22529-158502 + 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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