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Credit Risk (Narrative) (Details) | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2016 USD ($) customer counterparty | Sep. 30, 2016 counterparty | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Concentration Risk [Line Items] |  |  |  |
Gross credit exposure | $ 98,000,000 |  |  |
Additional collateral to be posted if the credit-related contingent features were triggered |  |  | $ 3,000,000 | $ 12,000,000
Amount of collateral posted | 0 |  | 0 |
Aggregate fair value of derivative instruments in a liability position and not fully collateralized with cash | 9,000,000 |  | $ 49,000,000 |
Virginia Electric and Power Company |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Gross credit exposure | 42,000,000 |  |  |
Investment Grade Counterparties |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Number of counterparties | counterparty |  | 0 |  |
Amount of exposure | $ 9,000,000 |  |  |
Investment Grade Counterparties | Virginia Electric and Power Company |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Number of counterparties | counterparty | 0 |  |  |
Amount of exposure | $ 6,000,000 |  |  |
Investment Grade Counterparties | Investment Grade |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration of credit risk (percentage) | 53.00% |  |  |
Investment Grade Counterparties | Investment Grade | Virginia Electric and Power Company |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration of credit risk (percentage) | 33.00% |  |  |
Customer Concentration Risk | Sales Revenue, Net | DTI |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration of credit risk (percentage) | 96.00% |  |  |
Number of customers | customer | 289 |  |  |
Customer Concentration Risk | Sales Revenue, Net | DTI | Ten Largest Customers |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration of credit risk (percentage) | 40.00% |  |  |
Number of customers | customer | 10 |  |  |
Customer Concentration Risk | Sales Revenue, Net | DTI | Thirty Largest Customers |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration of credit risk (percentage) | 70.00% |  |  |
Number of customers | customer | 30 |  |  |
Customer Concentration Risk | Sales Revenue, Net | East Ohio |  |  |  |
Concentration Risk [Line Items] |  |  |  |
Concentration of credit risk (percentage) | 98.00% |  |  |

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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=56946850&loc=SL5624258-113959 + Details
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- Definition The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features. + 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 (d) -URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624258-113959 + Details
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