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Employee Benefit Plans (Net Periodic Benefit (Credit) Cost and Amounts Recognized in Other Comprehensive Income and Regulatory Assets and Liabilities) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Pension Benefits |  |  |  |
Service cost |  | $ 162 | $ 157 | $ 138
Interest cost |  | 394 | 337 | 345
Expected return on plan assets |  | (708) | (663) | (639)
Amortization of prior service (credit) cost |  | 1 | 1 | 1
Amortization of net actuarial loss |  | 172 | 193 | 162
Settlements and curtailments |  | 72 | 0 | 0
Net periodic benefit (credit) cost |  | 93 | 25 | 7
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | 16 | 490 | 142
Prior service (credit) cost |  | 0 | 0 | 5
Settlements and curtailments |  | 6 | 0 | 1
Amortization of net actuarial loss |  | (172) | (193) | (162)
Amortization of prior service credit (cost) |  | (1) | (1) | (1)
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ (151) | $ 296 | $ (15)
Significant assumptions used to determine periodic cost: |  |  |  |
Expected long-term rate of return on plan assets |  |  | 8.75% | 8.75%
Weighted average rate of increase for compensation |  | 4.20% | 4.09% | 4.09%
Pension Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Service cost |  | $ 6 | $ 18 | $ 15
Interest cost |  | 11 | 29 | 30
Expected return on plan assets |  | (54) | (150) | (141)
Amortization of prior service (credit) cost |  | 0 | 0 | 0
Amortization of net actuarial loss |  | 7 | 19 | 16
Settlements and curtailments |  | 1 |  |
Net periodic benefit (credit) cost |  | (29) | (84) | (80)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | (46) | 207 | (75)
Prior service (credit) cost |  | 0 | 0 | 0
Amortization of net actuarial loss |  | (7) | (19) | (16)
Amortization of prior service credit (cost) |  | 0 | 0 | 0
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ (53) | $ 188 | $ (91)
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  |  | 3.81% | 4.50%
Expected long-term rate of return on plan assets |  | 8.65% | 8.75% | 8.75%
Weighted average rate of increase for compensation |  | 4.55% | 4.11% | 4.11%
Pension Benefits | Minimum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 3.57% | 3.80% | 3.31%
Expected long-term rate of return on plan assets |  | 7.00% |  |
Pension Benefits | Minimum | Dominion Energy Gas Holdings, LLC |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 4.10% |  |
Pension Benefits | Maximum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 4.43% | 3.81% | 4.50%
Expected long-term rate of return on plan assets |  | 8.65% |  |
Pension Benefits | Maximum | Dominion Energy Gas Holdings, LLC |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 4.42% |  |
Other Postretirement Benefits |  |  |  |
Service cost |  | $ 26 | $ 27 | $ 26
Interest cost |  | 68 | 56 | 60
Expected return on plan assets |  | (140) | (143) | (128)
Amortization of prior service (credit) cost |  | (52) | (52) | (51)
Amortization of net actuarial loss |  | 10 | 11 | 13
Settlements and curtailments |  | 42 | 0 | 0
Net periodic benefit (credit) cost |  | (46) | (101) | (80)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | (98) | 78 | 12
Prior service (credit) cost |  | 2 | (4) | (73)
Settlements and curtailments |  | 0 | 0 | 2
Amortization of net actuarial loss |  | (10) | (11) | (13)
Amortization of prior service credit (cost) |  | 52 | 52 | 51
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ (54) | $ 115 | $ (21)
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  |  | 3.76% |
Expected long-term rate of return on plan assets |  | 8.50% | 8.50% | 8.50%
Healthcare cost trend rate | [1] |  | 7.00% | 7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) | [1] | 5.00% | 5.00% | 5.00%
Year that the rate reaches the ultimate trend rate | [1] |  | 2022 | 2021
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC |  |  |  |
Service cost |  | $ 1 | $ 4 | $ 4
Interest cost |  | 5 | 11 | 12
Expected return on plan assets |  | (16) | (28) | (24)
Amortization of prior service (credit) cost |  | (5) | (4) | (3)
Amortization of net actuarial loss |  | 3 | 3 | 2
Settlements and curtailments |  | 1 |  |
Net periodic benefit (credit) cost |  | (11) | (14) | (9)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | (21) | 16 | 18
Prior service (credit) cost |  | 0 | (4) | (61)
Amortization of net actuarial loss |  | (3) | (3) | (2)
Amortization of prior service credit (cost) |  | 5 | 4 | 3
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ (19) | $ 13 | $ (42)
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  |  | 3.81% | 4.47%
Expected long-term rate of return on plan assets |  | 8.50% | 8.50% | 8.50%
Healthcare cost trend rate | [1] | 6.50% | 7.00% | 7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) | [1] | 5.00% | 5.00% | 5.00%
Year that the rate reaches the ultimate trend rate | [1] | 2025 | 2022 | 2021
Other Postretirement Benefits | Minimum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 4.05% |  | 3.92%
Healthcare cost trend rate | [1] | 6.50% |  |
Year that the rate reaches the ultimate trend rate | [1] | 2023 |  |
Other Postretirement Benefits | Minimum | Dominion Energy Gas Holdings, LLC |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 4.05% |  |
Other Postretirement Benefits | Maximum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 4.41% |  | 4.47%
Healthcare cost trend rate | [1] | 6.60% |  |
Year that the rate reaches the ultimate trend rate | [1] | 2025 |  |
Other Postretirement Benefits | Maximum | Dominion Energy Gas Holdings, LLC |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate |  | 4.37% |  |
[1] | Assumptions used to determine net periodic cost for the following year.

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- Definition Amount of (increase) decrease in accumulated benefit obligation of defined benefit plan from effects of settlement and curtailment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (r) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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