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Employee Benefit Plans (Summary of Changes in Pension and Other Postretirement Benefit Plans) (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Changes in fair value of plan assets: |  |  |  |
Actual return (loss) on plan assets |  | $ 1,600,000,000 | $ 534,000,000 |
Employer contributions |  | 0 |  |
Dominion Energy Gas Holdings, LLC |  |  |  |
Changes in fair value of plan assets: |  |  |  |
Actual return (loss) on plan assets |  | 335,000,000 | 130,000,000 |
Employer contributions |  | 0 |  |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | 8,132,000,000 | 6,391,000,000 |
Dominion Energy Questar Combination |  |  | 817,000,000 |
Service cost |  | 138,000,000 | 118,000,000 | $ 126,000,000
Interest cost |  | 345,000,000 | 317,000,000 | 287,000,000
Benefits paid |  | (323,000,000) | (286,000,000) |
Actuarial (gains) losses during the year |  | 830,000,000 | 784,000,000 |
Plan amendments | [1] | 5,000,000 |  |
Settlements and curtailments | [2] | (75,000,000) | (9,000,000) |
Benefit obligation at end of year |  | 9,052,000,000 | 8,132,000,000 | 6,391,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 7,016,000,000 | 6,166,000,000 |
Dominion Energy Questar Combination |  |  | 704,000,000 |
Actual return (loss) on plan assets |  | 1,327,000,000 | 426,000,000 |
Employer contributions |  | 118,000,000 | 15,000,000 |
Benefits paid |  | (323,000,000) | (286,000,000) |
Settlements | [2] | (76,000,000) | (9,000,000) |
Fair value of plan assets at end of year |  | 8,062,000,000 | 7,016,000,000 | 6,166,000,000
Funded status at end of year |  | (990,000,000) | (1,116,000,000) |
Noncurrent pension and other postretirement benefit assets |  | 1,117,000,000 | 930,000,000 |
Other current liabilities |  | (8,000,000) | (43,000,000) |
Noncurrent pension and other postretirement benefit liabilities |  | (2,099,000,000) | (2,003,000,000) |
Net amount recognized |  | $ (990,000,000) | $ (1,116,000,000) |
Changes in benefit obligation: |  |  |  |
Weighted average rate of increase for compensation |  | 4.09% | 4.09% |
Pension Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | $ 683,000,000 | $ 608,000,000 |
Service cost |  | 15,000,000 | 13,000,000 | 15,000,000
Interest cost |  | 30,000,000 | 30,000,000 | 27,000,000
Benefits paid |  | (33,000,000) | (32,000,000) |
Actuarial (gains) losses during the year |  | 78,000,000 | 64,000,000 |
Benefit obligation at end of year |  | 773,000,000 | 683,000,000 | 608,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 1,542,000,000 | 1,467,000,000 |
Actual return (loss) on plan assets |  | 294,000,000 | 107,000,000 |
Benefits paid |  | (33,000,000) | (32,000,000) |
Fair value of plan assets at end of year |  | 1,803,000,000 | 1,542,000,000 | 1,467,000,000
Funded status at end of year |  | 1,030,000,000 | 859,000,000 |
Noncurrent pension and other postretirement benefit assets |  | 1,030,000,000 | 859,000,000 |
Net amount recognized |  | $ 1,030,000,000 | $ 859,000,000 |
Changes in benefit obligation: |  |  |  |
Discount rate |  | 3.81% | 4.50% |
Weighted average rate of increase for compensation |  | 4.11% | 4.11% |
Pension Benefits | Minimum |  |  |  |
Changes in benefit obligation: |  |  |  |
Discount rate |  | 3.80% | 3.31% |
Pension Benefits | Maximum |  |  |  |
Changes in benefit obligation: |  |  |  |
Discount rate |  | 3.81% | 4.50% |
Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | $ 1,478,000,000 | $ 1,430,000,000 |
Dominion Energy Questar Combination |  |  | 85,000,000 |
Service cost |  | 26,000,000 | 31,000,000 | 40,000,000
Interest cost |  | 60,000,000 | 65,000,000 | 67,000,000
Benefits paid |  | (83,000,000) | (83,000,000) |
Actuarial (gains) losses during the year |  | 119,000,000 | 166,000,000 |
Plan amendments | [1] | (73,000,000) | (216,000,000) |
Settlements and curtailments | [2] | 2,000,000 |  |
Benefit obligation at end of year |  | 1,529,000,000 | 1,478,000,000 | 1,430,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 1,512,000,000 | 1,382,000,000 |
Dominion Energy Questar Combination |  |  | 45,000,000 |
Actual return (loss) on plan assets |  | 236,000,000 | 108,000,000 |
Employer contributions |  | 13,000,000 | 12,000,000 |
Benefits paid |  | (32,000,000) | (35,000,000) |
Fair value of plan assets at end of year |  | 1,729,000,000 | 1,512,000,000 | 1,382,000,000
Funded status at end of year |  | 200,000,000 | 34,000,000 |
Noncurrent pension and other postretirement benefit assets |  | 261,000,000 | 148,000,000 |
Other current liabilities |  |  | (5,000,000) |
Noncurrent pension and other postretirement benefit liabilities |  | (61,000,000) | (109,000,000) |
Net amount recognized |  | $ 200,000,000 | $ 34,000,000 |
Changes in benefit obligation: |  |  |  |
Discount rate |  | 3.76% |  |
Weighted average rate of increase for compensation |  |  | 3.29% |
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of year |  | $ 320,000,000 | $ 292,000,000 |
Service cost |  | 4,000,000 | 5,000,000 | 7,000,000
Interest cost |  | 12,000,000 | 14,000,000 | 14,000,000
Benefits paid |  | (19,000,000) | (19,000,000) |
Actuarial (gains) losses during the year |  | 34,000,000 | 28,000,000 |
Plan amendments | [1] | (61,000,000) |  |
Benefit obligation at end of year |  | 290,000,000 | 320,000,000 | 292,000,000
Changes in fair value of plan assets: |  |  |  |
Fair value of plan assets at beginning of year |  | 299,000,000 | 283,000,000 |
Actual return (loss) on plan assets |  | 41,000,000 | 23,000,000 |
Employer contributions |  | 12,000,000 | 12,000,000 |
Benefits paid |  | (19,000,000) | (19,000,000) |
Fair value of plan assets at end of year |  | 333,000,000 | 299,000,000 | $ 283,000,000
Funded status at end of year |  | 43,000,000 | (21,000,000) |
Noncurrent pension and other postretirement benefit assets |  | 57,000,000 |  |
Noncurrent pension and other postretirement benefit liabilities | [3] | (14,000,000) | (21,000,000) |
Net amount recognized |  | $ 43,000,000 | $ (21,000,000) |
Changes in benefit obligation: |  |  |  |
Discount rate |  | 3.76% | 4.47% |
Other Postretirement Benefits | Minimum |  |  |  |
Changes in benefit obligation: |  |  |  |
Discount rate |  |  | 3.92% |
Weighted average rate of increase for compensation |  | 3.95% |  |
Other Postretirement Benefits | Maximum |  |  |  |
Changes in benefit obligation: |  |  |  |
Discount rate |  |  | 4.47% |
Weighted average rate of increase for compensation |  | 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. 2016 amount relates primarily to a plan amendment that changed post-65 retiree medical coverage for certain current and future Local 50 retirees effective April 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. 2016 amount relates primarily to a settlement for certain executives.
[3] | Reflected in other deferred credits and other liabilities in Dominion Energy Gas' Consolidated Balance Sheets.

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