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Employee Benefit Plans (Summary of Changes in Pension and Other Postretirement Benefit Plans) (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Changes in fair value of plan assets: |  |  |  |
Actual return (loss) on plan assets |  | $ (605,000,000) | $ 1,600,000,000 |
Employer contributions |  | 0 |  |
Dominion Energy Gas Holdings, LLC |  |  |  |
Changes in fair value of plan assets: |  |  |  |
Actual return (loss) on plan assets |  | (129,000,000) | 335,000,000 |
Employer contributions |  | 0 |  |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | 9,052,000,000 | 8,132,000,000 |
Service cost |  | 157,000,000 | 138,000,000 | $ 118,000,000
Interest cost |  | 337,000,000 | 345,000,000 | 317,000,000
Benefits paid |  | (358,000,000) | (323,000,000) |
Actuarial (gains) losses during the year |  | (688,000,000) | 830,000,000 |
Plan amendments | [1] |  | 5,000,000 |
Settlements and curtailments | [2] |  | (75,000,000) |
Benefit obligation at end of year |  | 8,500,000,000 | 9,052,000,000 | 8,132,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 8,062,000,000 | 7,016,000,000 |
Actual return (loss) on plan assets |  | (513,000,000) | 1,327,000,000 |
Employer contributions |  | 6,000,000 | 118,000,000 |
Benefits paid |  | (358,000,000) | (323,000,000) |
Settlements | [2] |  | (76,000,000) |
Fair value of plan assets at end of year |  | 7,197,000,000 | 8,062,000,000 | 7,016,000,000
Funded status at end of year |  | (1,303,000,000) | (990,000,000) |
Noncurrent pension and other postretirement benefit assets |  | 1,003,000,000 | 1,117,000,000 |
Other current liabilities |  | (34,000,000) | (8,000,000) |
Noncurrent pension and other postretirement benefit liabilities |  | (2,272,000,000) | (2,099,000,000) |
Net amount recognized |  | $ (1,303,000,000) | $ (990,000,000) |
Significant assumptions used to determine benefit obligations |  |  |  |
Weighted average rate of increase for compensation |  | 4.32% | 4.09% |
Pension Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | $ 773,000,000 | $ 683,000,000 |
Service cost |  | 18,000,000 | 15,000,000 | 13,000,000
Interest cost |  | 29,000,000 | 30,000,000 | 30,000,000
Benefits paid |  | (34,000,000) | (33,000,000) |
Actuarial (gains) losses during the year |  | (56,000,000) | 78,000,000 |
Benefit obligation at end of year |  | 730,000,000 | 773,000,000 | 683,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 1,803,000,000 | 1,542,000,000 |
Actual return (loss) on plan assets |  | (113,000,000) | 294,000,000 |
Benefits paid |  | (34,000,000) | (33,000,000) |
Fair value of plan assets at end of year |  | 1,656,000,000 | 1,803,000,000 | 1,542,000,000
Funded status at end of year |  | 926,000,000 | 1,030,000,000 |
Noncurrent pension and other postretirement benefit assets |  | 926,000,000 | 1,030,000,000 |
Net amount recognized |  | $ 926,000,000 | $ 1,030,000,000 |
Significant assumptions used to determine benefit obligations |  |  |  |
Discount rate |  | 4.42% | 3.81% |
Weighted average rate of increase for compensation |  | 4.55% | 4.11% |
Pension Benefits | Minimum |  |  |  |
Significant assumptions used to determine benefit obligations |  |  |  |
Discount rate |  | 4.42% | 3.80% |
Pension Benefits | Maximum |  |  |  |
Significant assumptions used to determine benefit obligations |  |  |  |
Discount rate |  | 4.43% | 3.81% |
Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | $ 1,529,000,000 | $ 1,478,000,000 |
Service cost |  | 27,000,000 | 26,000,000 | 31,000,000
Interest cost |  | 56,000,000 | 60,000,000 | 65,000,000
Benefits paid |  | (87,000,000) | (83,000,000) |
Actuarial (gains) losses during the year |  | (158,000,000) | 119,000,000 |
Plan amendments | [1] | (4,000,000) | (73,000,000) |
Settlements and curtailments | [2] |  | 2,000,000 |
Benefit obligation at end of year |  | 1,363,000,000 | 1,529,000,000 | 1,478,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 1,729,000,000 | 1,512,000,000 |
Actual return (loss) on plan assets |  | (92,000,000) | 236,000,000 |
Employer contributions |  | 12,000,000 | 13,000,000 |
Benefits paid |  | (68,000,000) | (32,000,000) |
Fair value of plan assets at end of year |  | 1,581,000,000 | 1,729,000,000 | 1,512,000,000
Funded status at end of year |  | 218,000,000 | 200,000,000 |
Noncurrent pension and other postretirement benefit assets |  | 276,000,000 | 261,000,000 |
Other current liabilities |  | (2,000,000) |  |
Noncurrent pension and other postretirement benefit liabilities |  | (56,000,000) | (61,000,000) |
Net amount recognized |  | 218,000,000 | $ 200,000,000 |
Significant assumptions used to determine benefit obligations |  |  |  |
Discount rate |  |  | 3.76% |
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | 290,000,000 | $ 320,000,000 |
Service cost |  | 4,000,000 | 4,000,000 | 5,000,000
Interest cost |  | 11,000,000 | 12,000,000 | 14,000,000
Benefits paid |  | (18,000,000) | (19,000,000) |
Actuarial (gains) losses during the year |  | (27,000,000) | 34,000,000 |
Plan amendments | [1] | (4,000,000) | (61,000,000) |
Benefit obligation at end of year |  | 256,000,000 | 290,000,000 | 320,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 333,000,000 | 299,000,000 |
Actual return (loss) on plan assets |  | (16,000,000) | 41,000,000 |
Employer contributions |  | 12,000,000 | 12,000,000 |
Benefits paid |  | (18,000,000) | (19,000,000) |
Fair value of plan assets at end of year |  | 311,000,000 | 333,000,000 | $ 299,000,000
Funded status at end of year |  | 55,000,000 | 43,000,000 |
Noncurrent pension and other postretirement benefit assets |  | 63,000,000 | 57,000,000 |
Noncurrent pension and other postretirement benefit liabilities | [3] | (8,000,000) | (14,000,000) |
Net amount recognized |  | $ 55,000,000 | $ 43,000,000 |
Significant assumptions used to determine benefit obligations |  |  |  |
Discount rate |  | 4.37% | 3.76% |
Other Postretirement Benefits | Minimum |  |  |  |
Significant assumptions used to determine benefit obligations |  |  |  |
Discount rate |  | 4.37% |  |
Weighted average rate of increase for compensation |  | 4.30% | 3.95% |
Other Postretirement Benefits | Maximum |  |  |  |
Significant assumptions used to determine benefit obligations |  |  |  |
Discount rate |  | 4.38% |  |
Weighted average rate of increase for compensation |  | 4.55% | 4.11% |
[1] | 2017 amounts relate primarily to a plan amendment that changed post-65 retiree medical coverage for certain current and future Local 69 retirees effective July 1, 2017.
[2] | 2017 amount relates primarily to settlement and curtailment as a result of the voluntary and involuntary separation programs at Dominion Energy Questar.
[3] | Reflected in other deferred credits and other liabilities in Dominion Energy Gas' Consolidated Balance Sheets.

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