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Investments (Recorded Other-Than-Temporary Impairment Losses on Investments) (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other-than-temporary impairment losses for debt securities | $ 5 | $ 13 | $ 9
Virginia Electric and Power Company |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other-than-temporary impairment losses for debt securities | $ 2 | $ 8 | $ 6

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- Definition This item represents other-than-temporary impairment losses for fixed maturities. + References No definition available. + 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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- Details
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