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Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2019 USD ($) $ / MMBTU $ / MWh | Dec. 31, 2018 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | $ 209 | $ 294
Fair Value of Derivative Liabilities |  | 626 | 279
Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 83 | 93
Fair Value of Derivative Liabilities |  | 358 | 103
Fair Value, Measurements, Recurring |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 5,710 | 5,156
Total liabilities |  | 626 | 279
Fair Value, Measurements, Recurring | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 2,611 | 2,297
Total liabilities |  | 358 | 103
Fair Value, Measurements, Recurring | Commodity |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 188 | 250
Fair Value of Derivative Liabilities |  | 69 | 135
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 83 | 90
Fair Value of Derivative Liabilities |  | 26 | 15
Fair Value, Measurements, Recurring | Level 3 |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 84 | 70
Total liabilities |  | 9 | 6
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 81 | 66
Total liabilities |  | 4 | 6
Fair Value, Measurements, Recurring | Level 3 | Derivative Financial Instruments, Liabilities | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total liabilities |  | 4 |
Fair Value, Measurements, Recurring | Level 3 | Assets | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 81 |
Fair Value, Measurements, Recurring | Level 3 | Commodity |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 84 | 70
Fair Value of Derivative Liabilities |  | 9 | 6
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 81 | 66
Fair Value of Derivative Liabilities |  | 4 | $ 6
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 7 |
Fair Value of Derivative Liabilities |  | 3 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Derivative Financial Instruments, Liabilities | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Liabilities |  | 3 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Assets | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | $ 7 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Minimum | Derivative Financial Instruments, Liabilities | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | (4) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Minimum | Derivative Financial Instruments, Liabilities | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | (4) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Minimum | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | (1) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Minimum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | (1) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Maximum | Derivative Financial Instruments, Liabilities | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | 4 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Maximum | Derivative Financial Instruments, Liabilities | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | 4 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Maximum | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | 4 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Maximum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | 4 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Weighted Average | Derivative Financial Instruments, Liabilities | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | 0 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Weighted Average | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1],[2] | 1 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Weighted Average | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1],[2] | 1 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets | [3] | $ 76 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Assets | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets | [3] | $ 74 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Minimum | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | (2) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Minimum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | (2) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Maximum | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 6 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Maximum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 3 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Weighted Average | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1],[2] | (1) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Weighted Average | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1],[2] | (1) |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | $ 1 |
Fair Value of Derivative Liabilities |  | 6 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Derivative Financial Instruments, Liabilities | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Liabilities |  | $ 1 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Derivative Financial Instruments, Liabilities | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 1 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Derivative Financial Instruments, Liabilities | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 1 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Derivative Financial Instruments, Liabilities | Price Volatility [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 2.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Derivative Financial Instruments, Liabilities | Price Volatility [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 20.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 2 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Assets | Price Volatility [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 2.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Derivative Financial Instruments, Liabilities | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 8 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Derivative Financial Instruments, Liabilities | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 7 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Derivative Financial Instruments, Liabilities | Price Volatility [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 71.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Derivative Financial Instruments, Liabilities | Price Volatility [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 71.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 12 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Assets | Price Volatility [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 34.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Weighted Average | Derivative Financial Instruments, Liabilities | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1],[2] | 3 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Weighted Average | Derivative Financial Instruments, Liabilities | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1],[2] | 3 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Weighted Average | Derivative Financial Instruments, Liabilities | Price Volatility [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [2],[4] | 29.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Weighted Average | Derivative Financial Instruments, Liabilities | Price Volatility [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [2],[4] | 38.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Weighted Average | Assets | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1],[2] | 4 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Weighted Average | Assets | Price Volatility [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [2],[4] | 19.00% |
[1] | Represents market prices beyond defined terms for Levels 1 and 2.
[2] | Averages weighted by volume.
[3] | Includes basis.
[4] | Represents volatilities unrepresented in published markets.

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