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Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 USD ($) $ / MMBTU $ / MWh | Dec. 31, 2017 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 244 |  | $ 307
Fair Value of Derivative Liabilities |  | 90 |  | 284
Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 129 | [1] | 166
Fair Value of Derivative Liabilities |  | 23 |  | 66
Fair Value, Measurements, Recurring | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 156 |  | 258
Fair Value of Derivative Liabilities |  | 31 |  | 197
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 123 |  | 166
Fair Value of Derivative Liabilities |  | 9 |  | 9
Fair Value, Measurements, Recurring | Level 3 |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 122 |  |
Fair Value of Derivative Liabilities |  | 2 |  |
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 119 |  |
Fair Value of Derivative Liabilities |  | 2 |  |
Fair Value, Measurements, Recurring | Level 3 | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 122 |  | 157
Fair Value of Derivative Liabilities |  | 2 |  | 7
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 119 |  | 152
Fair Value of Derivative Liabilities |  | 2 |  | $ 5
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 9 |  |
Fair Value of Derivative Liabilities |  | 2 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Liabilities | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Liabilities |  | 2 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 8 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Minimum | Liabilities |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | (5) |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Minimum | Liabilities | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | (5) |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Minimum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | (1) |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Minimum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | (1) |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Maximum | Liabilities |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 6 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Maximum | Liabilities | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 6 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Maximum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 6 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Maximum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 6 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Weighted Average | Liabilities |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2],[3] | 0 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Weighted Average | Liabilities | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2],[3] | 0 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Weighted Average | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2],[3] | 1 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | FTRs | Commodity | Weighted Average | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2],[3] | 1 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets | [4] | $ 83 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets | [4] | $ 81 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity | Minimum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | (2) |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity | Minimum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | (2) |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity | Maximum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | 6 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity | Maximum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | 6 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity | Weighted Average | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2],[3] | 0 |  |
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Natural Gas | Commodity | Weighted Average | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2],[3] | (1) |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 29 |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 29 |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity | Minimum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 23 |  |
Price volatility (percentage) | [5] | 7.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity | Minimum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 23 |  |
Price volatility (percentage) | [5] | 7.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity | Maximum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 49 |  |
Price volatility (percentage) | [5] | 63.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity | Maximum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2] | 49 |  |
Price volatility (percentage) | [5] | 63.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity | Weighted Average | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2],[3] | 35 |  |
Price volatility (percentage) | [3],[5] | 27.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Electricity | Electricity | Weighted Average | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [2],[3] | 35 |  |
Price volatility (percentage) | [3],[5] | 27.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 1 |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 1 |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options | Minimum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | 2 |  |
Price volatility (percentage) | [5] | 14.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options | Minimum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | 2 |  |
Price volatility (percentage) | [5] | 14.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options | Maximum | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | 6 |  |
Price volatility (percentage) | [5] | 29.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options | Maximum | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2] | 6 |  |
Price volatility (percentage) | [5] | 29.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options | Weighted Average | Assets |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2],[3] | 3 |  |
Price volatility (percentage) | [3],[5] | 23.00% |  |
Fair Value, Measurements, Recurring | Level 3 | Option model | Natural Gas | Physical options | Weighted Average | Assets | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [2],[3] | 3 |  |
Price volatility (percentage) | [3],[5] | 23.00% |  |
[1] | Noncurrent derivative assets are presented in other deferred charges and other assets in Virginia Power's Consolidated Balance Sheets.
[2] | Represents market prices beyond defined terms for Levels 1 and 2.
[3] | Averages weighted by volume.
[4] | Includes basis.
[5] | Represents volatilities unrepresented in published markets.

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