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Credit Risk (Narrative) (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2017 USD ($) counterparty | Jun. 30, 2016 USD ($) | Jun. 30, 2017 USD ($) counterparty | Jun. 30, 2016 USD ($) | Dec. 31, 2016 USD ($)
Concentration Risk and Guarantor Obligations [Line Items] |  |  |  |  |  |
Gross credit exposure |  |  |  | $ 69 |  |
Operating Revenue |  | $ 2,813 | $ 2,598 | 6,197 | $ 5,519 |
Additional collateral to be posted if the credit related contingent features were triggered |  |  |  |  |  | $ 3
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position |  |  |  |  |  | $ 9
Maximum |  |  |  |  |  |
Concentration Risk and Guarantor Obligations [Line Items] |  |  |  |  |  |
Additional collateral to be posted if the credit related contingent features were triggered |  | 1 |  | 1 |  |
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position |  | $ 1 |  | $ 1 |  |
Credit Concentration Risk |  |  |  |  |  |
Concentration Risk and Guarantor Obligations [Line Items] |  |  |  |  |  |
Number of counterparties | counterparty |  | 0 |  | 0 |  |
Amount of exposure for single counterparty |  |  |  | $ 17 |  |
Credit Concentration Risk | Investment Grade | Investment Grade Counterparty |  |  |  |  |  |
Concentration Risk and Guarantor Obligations [Line Items] |  |  |  |  |  |
Concentration risk, percentage (percentage) |  |  |  | 74.00% |  |
Virginia Electric and Power Company |  |  |  |  |  |
Concentration Risk and Guarantor Obligations [Line Items] |  |  |  |  |  |
Electric distribution poles renting space, settlement charge |  | $ 16 |  |  |  |
Electric distribution poles renting space, settlement charge, net of tax |  | 10 |  |  |  |
Operating Revenue | [1] | $ 1,747 | $ 1,776 | $ 3,578 | $ 3,666 |
Virginia Electric and Power Company | Credit Concentration Risk | Wholesale Customers | Sales to wholesale customers |  |  |  |  |  |
Concentration Risk and Guarantor Obligations [Line Items] |  |  |  |  |  |
Number of counterparties | counterparty |  | 0 |  | 0 |  |
Operating Revenue |  |  |  | $ 17 |  |
Amount of exposure related to sales to wholesale customers for single counterparty |  |  |  | $ 4 |  |
Virginia Electric and Power Company | Credit Concentration Risk | Investment Grade | Investment Grade Counterparty |  |  |  |  |  |
Concentration Risk and Guarantor Obligations [Line Items] |  |  |  |  |  |
Concentration risk, percentage (percentage) |  |  |  | 47.00% |  |
[1] | See Note 17 for amounts attributable to affiliates.

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- Definition The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959 + Details
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