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Employee Benefit Plans (Narrative) (Detail) - USD ($) |  |  |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2017 | Jun. 30, 2017 | Jan. 31, 2017 | Dec. 31, 2017 | Mar. 31, 2017 | Sep. 30, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2019
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Actual return (loss) on plan assets |  |  |  |  |  |  | $ (605,000,000) | $ 1,600,000,000 |  |
Expected return on pension and other postretirement plan assets |  |  |  |  |  |  | 806,000,000 | 767,000,000 |  |
Accumulated benefit obligation |  |  |  | $ 8,200,000,000 |  |  | 7,800,000,000 | 8,200,000,000 |  |
Contributions to qualified defined benefit pension plans |  |  |  |  |  |  | 0 |  |  |
Contributions to qualified defined benefit pension plans in 2019 |  |  |  |  |  |  | 21,000,000 |  |  |
Contribution to voluntary employees beneficiary association |  |  |  |  |  |  | 12,000,000 | 12,000,000 |  |
Defined contribution plan, employer matching contributions |  |  |  |  |  |  | $ 51,000,000 | 45,000,000 | $ 44,000,000 |
Special Termination Benefits | Organizational Design Initiative |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Organizational design initiative |  |  |  |  |  |  |  |  | 65,000,000 |
Organizational design initiative, after tax |  |  |  |  |  |  |  |  | 40,000,000 |
Common and Preferred Stocks |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, actual plan asset allocation percentages |  |  |  |  |  |  | 28.00% |  |  |
Non-U.S.Equity |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, actual plan asset allocation percentages |  |  |  |  |  |  | 18.00% |  |  |
Fixed Income |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, actual plan asset allocation percentages |  |  |  |  |  |  | 35.00% |  |  |
Real Estate Funds |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, actual plan asset allocation percentages |  |  |  |  |  |  | 3.00% |  |  |
Other Alternative Investments |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, actual plan asset allocation percentages |  |  |  |  |  |  | 16.00% |  |  |
Scenario, Forecast |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Pension or other postretirement plan assets to be returned |  |  |  |  |  |  |  |  |  | $ 0
Pension Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Actual return (loss) on plan assets |  |  |  |  |  |  | $ (513,000,000) | 1,327,000,000 |  |
Expected return on pension and other postretirement plan assets |  |  |  |  |  |  | 663,000,000 | 639,000,000 | 573,000,000 |
Net periodic benefit cost |  |  |  |  |  |  | 25,000,000 | 7,000,000 | $ (25,000,000) |
Decrease in accumulated postretirement benefit obligation |  |  |  | 75,000,000 |  |  |  |  |  |
Discount rate percentage | 4.05% | 4.05% | 4.51% |  |  |  |  |  | 4.46% |
Contributions to qualified defined benefit pension plans |  |  |  |  |  |  | 6,000,000 | 118,000,000 |  |
Other Postretirement Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Actual return (loss) on plan assets |  |  |  |  |  |  | (92,000,000) | 236,000,000 |  |
Expected return on pension and other postretirement plan assets |  |  |  |  |  |  | 143,000,000 | 128,000,000 | $ 118,000,000 |
Net periodic benefit cost |  |  |  |  |  |  | $ (101,000,000) | $ (80,000,000) | $ (49,000,000) |
Decrease in accumulated postretirement benefit obligation |  |  |  | $ 2,000,000 |  |  |  |  |  |
Discount rate percentage |  |  |  |  |  |  | 3.76% |  |  |
Discount rate percentage |  |  |  | 3.76% |  |  |  | 3.76% |  |
Contributions to qualified defined benefit pension plans |  |  |  |  |  |  | $ 12,000,000 | $ 13,000,000 |  |
Medical Coverage for Local retirees |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in accumulated postretirement benefit obligation |  |  |  |  | $ 73,000,000 | $ 37,000,000 |  |  |  |
Discount rate percentage |  |  |  |  | 4.30% | 3.71% |  |  |  |
Charge recorded from plan amendment and remeasurement |  |  |  |  |  | $ 9,000,000 |  |  |  |
Collective Bargaining Agreement |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Period for experience study of employee demographics |  |  |  |  |  |  |  |  | 5 years |
Net periodic benefit cost |  |  |  |  |  |  |  | 42,000,000 |  |
Charge recorded from plan amendment and remeasurement |  |  |  |  | $ 7,000,000 |  |  |  |  |
Charge recorded from plan amendment and remeasurement, after tax |  |  |  |  | 4,000,000 |  |  |  |  |
Collective Bargaining Agreement | Pension Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Increase in the pension and postretirement benefit obligations |  |  |  |  |  |  |  |  | $ 290,000,000 |
Collective Bargaining Agreement | Other Postretirement Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Increase in the pension and postretirement benefit obligations |  |  |  |  |  |  |  |  | 38,000,000 |
Dominion Energy Gas Holdings, LLC |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Actual return (loss) on plan assets |  |  |  |  |  |  | (129,000,000) | 335,000,000 |  |
Expected return on pension and other postretirement plan assets |  |  |  |  |  |  | 178,000,000 | 165,000,000 |  |
Accumulated benefit obligation |  |  |  | $ 724,000,000 |  |  | 689,000,000 | 724,000,000 |  |
Contributions to qualified defined benefit pension plans |  |  |  |  |  |  | 0 |  |  |
Contributions to qualified defined benefit pension plans in 2019 |  |  |  |  |  |  | 0 |  |  |
Expected contribution to voluntary employees beneficiary association |  |  |  |  |  |  | 12,000,000 |  |  |
Defined contribution plan, employer matching contributions |  |  |  |  |  |  | 8,000,000 | 8,000,000 | 7,000,000 |
Dominion Energy Gas Holdings, LLC | Other operations and maintenance | Dominion Energy Retiree Health And Welfare Plan [Member] | Multiemployer Plans, Postretirement Benefit |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Net periodic benefit cost |  |  |  |  |  |  | (8,000,000) | (6,000,000) | (4,000,000) |
Dominion Energy Gas Holdings, LLC | Special Termination Benefits | Organizational Design Initiative |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Organizational design initiative |  |  |  |  |  |  |  |  | 6,000,000 |
Organizational design initiative, after tax |  |  |  |  |  |  |  |  | 4,000,000 |
Dominion Energy Gas Holdings, LLC | Scenario, Forecast |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Pension or other postretirement plan assets to be returned |  |  |  |  |  |  |  |  |  | $ 0
Dominion Energy Gas Holdings, LLC | Pension Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Actual return (loss) on plan assets |  |  |  |  |  |  | (113,000,000) | 294,000,000 |  |
Expected return on pension and other postretirement plan assets |  |  |  |  |  |  | 150,000,000 | 141,000,000 | 134,000,000 |
Net periodic benefit cost |  |  |  |  |  |  | $ (84,000,000) | $ (80,000,000) | $ (78,000,000) |
Discount rate percentage |  |  |  |  |  |  | 3.81% | 4.50% | 4.99% |
Discount rate percentage |  |  |  | 3.81% |  |  | 4.42% | 3.81% |  |
Dominion Energy Gas Holdings, LLC | Pension Benefits | Other operations and maintenance |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Net periodic benefit cost |  |  |  |  |  |  | $ (35,000,000) | $ (35,000,000) | $ (44,000,000) |
Dominion Energy Gas Holdings, LLC | Other Postretirement Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Actual return (loss) on plan assets |  |  |  |  |  |  | (16,000,000) | 41,000,000 |  |
Expected return on pension and other postretirement plan assets |  |  |  |  |  |  | 28,000,000 | 24,000,000 | 23,000,000 |
Net periodic benefit cost |  |  |  |  |  |  | $ (14,000,000) | $ (9,000,000) | $ (2,000,000) |
Discount rate percentage |  |  |  |  |  |  | 3.81% | 4.47% | 4.93% |
Discount rate percentage |  |  |  | 3.76% |  |  | 4.37% | 3.76% |  |
Contributions to qualified defined benefit pension plans |  |  |  |  |  |  | $ 12,000,000 | $ 12,000,000 |  |
Dominion Energy Gas Holdings, LLC | Medical Coverage for Local retirees |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in accumulated postretirement benefit obligation |  |  |  |  | 61,000,000 |  |  |  |  |
Dominion Energy Gas Holdings, LLC | Collective Bargaining Agreement |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Charge recorded from plan amendment and remeasurement |  |  |  |  | 6,000,000 |  |  |  |  |
Charge recorded from plan amendment and remeasurement, after tax |  |  |  |  | $ 4,000,000 |  |  |  |  |
Dominion Energy Gas Holdings, LLC | Collective Bargaining Agreement | Pension Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Increase in the pension and postretirement benefit obligations |  |  |  |  |  |  |  |  | $ 24,000,000 |
Dominion Energy Gas Holdings, LLC | Collective Bargaining Agreement | Other Postretirement Benefits |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Increase in the pension and postretirement benefit obligations |  |  |  |  |  |  |  |  | 9,000,000 |
Virginia Electric and Power Company |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Defined contribution plan, employer matching contributions |  |  |  |  |  |  | 20,000,000 | 19,000,000 | 19,000,000 |
Virginia Electric and Power Company | Other operations and maintenance | Dominion Energy Retiree Health And Welfare Plan [Member] | Multiemployer Plans, Postretirement Benefit |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Net periodic benefit cost |  |  |  |  |  |  | (51,000,000) | (42,000,000) | (29,000,000) |
Virginia Electric and Power Company | Net Income Loss From Discontinued operations | Dominion Energy Retiree Health And Welfare Plan [Member] |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Net periodic benefit cost |  |  |  |  |  |  | (2,000,000) | (2,000,000) | (1,000,000) |
Virginia Electric and Power Company | Special Termination Benefits | Organizational Design Initiative |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Organizational design initiative |  |  |  |  |  |  |  |  | 33,000,000 |
Organizational design initiative, after tax |  |  |  |  |  |  |  |  | 20,000,000 |
Virginia Electric and Power Company | Pension Benefits | Other operations and maintenance |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Net periodic benefit cost |  |  |  |  |  |  | 126,000,000 | 110,000,000 | 79,000,000 |
Virginia Electric and Power Company | Pension Benefits | Net Income Loss From Discontinued operations |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |
Net periodic benefit cost |  |  |  |  |  |  | $ (21,000,000) | $ (20,000,000) | $ (25,000,000) |

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