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Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Detail) $ in Millions | Dec. 31, 2018 USD ($)
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Schedule of Held-to-maturity Securities [Line Items] |
Due in one year or less | $ 167
Due after one year through five years | 389
Due after five years through ten years | 376
Due after ten years | 672
Total | 1,604
Virginia Electric and Power Company |
Schedule of Held-to-maturity Securities [Line Items] |
Due in one year or less | 54
Due after one year through five years | 156
Due after five years through ten years | 210
Due after ten years | 358
Total | $ 778

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