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Investments (Marketable Equity and Debt Securities and Cash Equivalents (Classified as Available-for-sale) and Cost Method Investments in Decommissioning Trust Funds) (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Investment Holdings [Line Items] |  |  |
Total Unrealized Gains | [1] | $ 1,443 | $ 1,258
Total Unrealized Losses | [1],[2] | (12) | (11)
Nuclear decommissioning trust funds |  | 4,484 | 4,183
Total Amortized Cost |  | 3,053 | 2,936
Net assets related to pending sales and purchases of securities |  | 9 | 12
Fair value of securities in an unrealized loss position |  | 576 | 592
Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Other investments and securities, at cost |  | 1,473 | 1,404
Total Unrealized Gains | [3] | 639 | 548
Total Unrealized Losses | [3],[4] | (6) | (7)
Nuclear decommissioning trust funds |  | 2,106 | 1,945
Net assets related to pending sales and purchases of securities |  | 7 | 8
Fair value of securities in an unrealized loss position |  | 287 | 281
Cost method investments |  |  |
Investment Holdings [Line Items] |  |  |
Other investments and securities, at cost |  | 69 | 70
Total Unrealized Gains | [1] | 0 | 0
Total Unrealized Losses | [1] | 0 | 0
Nuclear decommissioning trust funds |  | 69 | 70
Cost method investments | Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Other investments and securities, at cost |  | 69 | 70
Total Unrealized Gains | [3] | 0 | 0
Total Unrealized Losses | [3] | 0 | 0
Nuclear decommissioning trust funds |  | 69 | 70
Cash equivalents and other |  |  |
Investment Holdings [Line Items] |  |  |
Other investments and securities, at cost | [5] | 12 | 14
Total Unrealized Gains | [1],[5] | 0 | 0
Total Unrealized Losses | [1],[5] | 0 | 0
Nuclear decommissioning trust funds | [5] | 12 | 14
Cash equivalents and other | Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost | [6] | 7 | 8
Total Unrealized Gains | [3],[6] | 0 | 0
Total Unrealized Losses | [3],[6] | 0 | 0
Nuclear decommissioning trust funds | [6] | 7 | 8
Corporate debt instruments |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 478 | 436
Total Unrealized Gains | [1] | 13 | 11
Total Unrealized Losses | [1] | (4) | (7)
Nuclear decommissioning trust funds |  | 487 | 440
Corporate debt instruments | Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 274 | 238
Total Unrealized Gains | [3] | 6 | 5
Total Unrealized Losses | [3] | (4) | (5)
Nuclear decommissioning trust funds |  | 276 | 238
Government securities |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 978 | 962
Total Unrealized Gains | [1] | 22 | 30
Total Unrealized Losses | [1] | (8) | (4)
Nuclear decommissioning trust funds |  | 992 | 988
Government securities | Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 420 | 421
Total Unrealized Gains | [3] | 9 | 15
Total Unrealized Losses | [3] | (2) | (2)
Nuclear decommissioning trust funds |  | 427 | 434
Common/collective trust funds |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 67 | 100
Total Unrealized Gains | [1] | 0 | 0
Total Unrealized Losses | [1] | 0 | 0
Nuclear decommissioning trust funds |  | 67 | 100
Common/collective trust funds | Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 26 | 34
Total Unrealized Gains | [3] | 0 | 0
Total Unrealized Losses | [3] | 0 | 0
Nuclear decommissioning trust funds |  | 26 | 34
U.S. | Equity securities: |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 1,449 | 1,354
Total Unrealized Gains | [1] | 1,408 | 1,217
Total Unrealized Losses | [1] | 0 | 0
Nuclear decommissioning trust funds |  | 2,857 | 2,571
U.S. | Equity securities: | Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Amortized Cost |  | 677 | 633
Total Unrealized Gains | [3] | 624 | 528
Total Unrealized Losses | [3] | 0 | 0
Nuclear decommissioning trust funds |  | $ 1,301 | $ 1,161
[1] | Included in AOCI and the nuclear decommissioning trust regulatory liability as discussed in Note 2.
[2] | fair value of securities in an unrealized loss position was $576 million and $592 million at December 31, 2016 and 2015, respectively.
[3] | Included in AOCI and the nuclear decommissioning trust regulatory liability as discussed in Note 2.
[4] | The fair value of securities in an unrealized loss position was $287 million and $281 million at December 31, 2016 and 2015, respectively.
[5] | Includes pending sales of securities of $9 million and $12 million at December 31, 2016 and 2015, respectively.
[6] | Includes pending sales of securities of $7 million and $8 million at December 31, 2016 and 2015, respectively.

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- Definition Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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