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Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2020 USD ($) $ / MMBTU $ / MWh | Dec. 31, 2019 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | $ 252 | $ 93
Fair Value of Derivative Liabilities |  | 776 | 740
Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 145 | 24
Fair Value of Derivative Liabilities |  | 491 | 466
Fair Value, Measurements, Recurring |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 6,303 | 5,963
Total liabilities |  | 776 | 740
Fair Value, Measurements, Recurring | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 2,925 | 2,748
Total liabilities |  | 491 | 466
Fair Value, Measurements, Recurring | Commodity |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 186 | 74
Fair Value of Derivative Liabilities |  | 51 | 131
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 145 | 22
Fair Value of Derivative Liabilities |  | 16 | 103
Fair Value, Measurements, Recurring | Level 3 |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 137 | 19
Total liabilities |  | 10 | 56
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Total assets |  | 137 | 19
Total liabilities |  | 10 | 56
Fair Value, Measurements, Recurring | Level 3 | Commodity |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 137 | 19
Fair Value of Derivative Liabilities |  | 10 | 56
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 137 | 19
Fair Value of Derivative Liabilities |  | 10 | $ 56
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 |  | 32 |
Fair Value of Derivative Liabilities |  | 10 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | 32 |
Fair Value of Derivative Liabilities |  | $ 10 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Minimum | Liabilities | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | (5) |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Minimum | Liabilities | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1] | (5) |
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 | 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 | 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] | 5 |
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] | 5 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Weighted Average | Liabilities | Market Price [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1],[2] | 0 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | FTRs [Member] | Commodity | Weighted Average | Liabilities | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MWh | [1],[2] | 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] | $ 102 |
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow [Member] | Natural Gas | Commodity | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets | [3] | $ 102 |
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] | 3 |
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 |  | $ 3 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Fair Value of Derivative Assets |  | $ 3 |
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] | 1 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Assets | 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 | Assets | Price Volatility [Member] |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 19.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Minimum | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 19.00% |
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] | 6 |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Market Price | $ / MMBTU | [1] | 6 |
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] | 61.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Maximum | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [4] | 61.00% |
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 | Market Price [Member] | Virginia Electric and Power Company |  |  |
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] | 35.00% |
Fair Value, Measurements, Recurring | Level 3 | Option Model [Member] | Natural Gas | Physical Options [Member] | Weighted Average | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |
Price volatility (percentage) | [2],[4] | 35.00% |
[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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