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Employee Benefit Plans (Fair values of pension and post retirement plan assets by asset category) (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total investments |  | $ 1,279 | $ 1,378 |
Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total investments | [1] | 1,775 | 1,828 |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 7,197 | 8,062 | $ 7,016
Pension Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,656 | 1,803 | 1,542
Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,581 | 1,729 | 1,512
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 311 | 333 | $ 299
Collective Bargaining Agreement | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 4,424 | 4,878 |
Total recorded at NAV | [2] | 2,762 | 3,169 |
Total investments | [3] | 7,186 | 8,047 |
Collective Bargaining Agreement | Pension Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,017 | 1,090 |
Total recorded at NAV | [2] | 636 | 709 |
Total investments | [4] | 1,653 | 1,799 |
Collective Bargaining Agreement | Pension Benefits | Cash equivalents and other |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 18 | 18 |
Collective Bargaining Agreement | Pension Benefits | Cash equivalents and other | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 4 | 4 |
Collective Bargaining Agreement | Pension Benefits | US Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,645 | 1,902 |
Collective Bargaining Agreement | Pension Benefits | US Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 378 | 425 |
Collective Bargaining Agreement | Pension Benefits | Foreign Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,061 | 1,151 |
Collective Bargaining Agreement | Pension Benefits | Foreign Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 244 | 257 |
Collective Bargaining Agreement | Pension Benefits | Insurance contracts |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 318 | 352 |
Collective Bargaining Agreement | Pension Benefits | Insurance contracts | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 73 | 79 |
Collective Bargaining Agreement | Pension Benefits | Corporate debt instruments |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 752 | 770 |
Collective Bargaining Agreement | Pension Benefits | Corporate debt instruments | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 173 | 172 |
Collective Bargaining Agreement | Pension Benefits | Government securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 630 | 685 |
Collective Bargaining Agreement | Pension Benefits | Government securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 145 | 153 |
Collective Bargaining Agreement | Pension Benefits | Common/collective trust funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 1,849 | 2,272 |
Collective Bargaining Agreement | Pension Benefits | Common/collective trust funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 425 | 509 |
Collective Bargaining Agreement | Pension Benefits | Real Estate Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 108 | 111 |
Collective Bargaining Agreement | Pension Benefits | Real Estate Funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 25 | 25 |
Collective Bargaining Agreement | Pension Benefits | Private Equity Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 633 | 606 |
Collective Bargaining Agreement | Pension Benefits | Private Equity Funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 146 | 135 |
Collective Bargaining Agreement | Pension Benefits | Fixed Income Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 155 | 161 |
Collective Bargaining Agreement | Pension Benefits | Fixed Income Funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 36 | 36 |
Collective Bargaining Agreement | Pension Benefits | Hedge Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 17 | 19 |
Collective Bargaining Agreement | Pension Benefits | Hedge Funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 4 | 4 |
Collective Bargaining Agreement | Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 829 | 944 |
Total recorded at NAV | [2] | 751 | 783 |
Total investments | [5] | 1,580 | 1,727 |
Collective Bargaining Agreement | Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 143 | 163 |
Total recorded at NAV | [2] | 168 | 170 |
Total investments |  | 311 | 333 |
Collective Bargaining Agreement | Other Postretirement Benefits | Cash equivalents and other |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 2 | 3 |
Collective Bargaining Agreement | Other Postretirement Benefits | US Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 554 | 636 |
Collective Bargaining Agreement | Other Postretirement Benefits | US Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 113 | 130 |
Collective Bargaining Agreement | Other Postretirement Benefits | Foreign Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 170 | 196 |
Collective Bargaining Agreement | Other Postretirement Benefits | Foreign Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 30 | 33 |
Collective Bargaining Agreement | Other Postretirement Benefits | Insurance contracts |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 19 | 21 |
Collective Bargaining Agreement | Other Postretirement Benefits | Corporate debt instruments |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 45 | 46 |
Collective Bargaining Agreement | Other Postretirement Benefits | Government securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 39 | 42 |
Collective Bargaining Agreement | Other Postretirement Benefits | Common/collective trust funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 650 | 689 |
Collective Bargaining Agreement | Other Postretirement Benefits | Common/collective trust funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 148 | 154 |
Collective Bargaining Agreement | Other Postretirement Benefits | Real Estate Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 10 | 9 |
Collective Bargaining Agreement | Other Postretirement Benefits | Real Estate Funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 2 | 1 |
Collective Bargaining Agreement | Other Postretirement Benefits | Private Equity Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 80 | 73 |
Collective Bargaining Agreement | Other Postretirement Benefits | Private Equity Funds | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 18 | 15 |
Collective Bargaining Agreement | Other Postretirement Benefits | Fixed Income Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 10 | 11 |
Collective Bargaining Agreement | Other Postretirement Benefits | Hedge Funds |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at NAV | [2] | 1 | 1 |
Level 1 | Collective Bargaining Agreement | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 2,771 | 3,121 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 637 | 697 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Cash equivalents and other |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 17 | 18 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Cash equivalents and other | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 4 | 4 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | US Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,645 | 1,902 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | US Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 378 | 425 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Foreign Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,061 | 1,151 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Foreign Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 244 | 257 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Corporate debt instruments |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 23 | 41 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Corporate debt instruments | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 5 | 9 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Government securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 25 | 9 |
Level 1 | Collective Bargaining Agreement | Pension Benefits | Government securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 6 | 2 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 728 | 836 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 143 | 163 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | Cash equivalents and other |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1 | 1 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | US Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 554 | 636 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | US Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 113 | 130 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | Foreign Equity Securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 170 | 196 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | Foreign Equity Securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 30 | 33 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | Corporate debt instruments |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1 | 2 |
Level 1 | Collective Bargaining Agreement | Other Postretirement Benefits | Government securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 2 | 1 |
Level 2 | Collective Bargaining Agreement | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1,653 | 1,757 |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 380 | 393 |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Cash equivalents and other |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1 |  |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Insurance contracts |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 318 | 352 |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Insurance contracts | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 73 | 79 |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Corporate debt instruments |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 729 | 729 |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Corporate debt instruments | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 168 | 163 |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Government securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 605 | 676 |
Level 2 | Collective Bargaining Agreement | Pension Benefits | Government securities | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 139 | 151 |
Level 2 | Collective Bargaining Agreement | Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 101 | 108 |
Level 2 | Collective Bargaining Agreement | Other Postretirement Benefits | Cash equivalents and other |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 1 | 2 |
Level 2 | Collective Bargaining Agreement | Other Postretirement Benefits | Insurance contracts |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 19 | 21 |
Level 2 | Collective Bargaining Agreement | Other Postretirement Benefits | Corporate debt instruments |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | 44 | 44 |
Level 2 | Collective Bargaining Agreement | Other Postretirement Benefits | Government securities |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total recorded at fair value |  | $ 37 | $ 41 |
[1] | See Note 24 for amounts attributable to related parties.
[2] | These investments that are measured at fair value using the NAV per share (or its equivalent) as a practical expedient which are not required to be categorized in the fair value hierarchy.
[3] | Excludes net assets related to pending sales of securities of $12 million, net accrued income of $21 million, and includes net assets related to pending purchases of securities of $22 million at December 31, 2018. Excludes net assets related to pending sales of securities of $11 million, net accrued income of $19 million, and includes net assets related to pending purchases of securities of $15 million at December 31, 2017.
[4] | Excludes net assets related to pending sales of securities of $3 million, net accrued income of $5 million, and includes net assets related to pending purchases of securities of $5 million at December 31, 2018. Excludes net assets related to pending sales of securities of $3 million, net accrued income of $4 million, and includes net assets related to pending purchases of securities of $3 million at December 31, 2017.
[5] | Excludes net assets related to pending sales of securities of $1 million, net accrued income of $2 million, and includes net assets related to pending purchases of securities of $2 million at December 31, 2018. Excludes net assets related to pending sales of securities of $1 million, net accrued income of $2 million, and includes net assets related to pending purchases of securities of $1 million at December 31, 2017.

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