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Employee Benefit Plans (Net Periodic Benefit (Credit) Cost and Amounts Recognized in Other Comprehensive Income and Regulatory Assets and Liabilities) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected return on plan assets |  | $ (691) | $ (648) |
Dominion Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected return on plan assets |  | (157) | (150) |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost |  | 118 | 126 | $ 114
Interest cost |  | 317 | 287 | 290
Expected return on plan assets |  | (573) | (531) | (499)
Amortization of prior service (credit) cost |  | 1 | 2 | 3
Amortization of net actuarial loss |  | 111 | 160 | 111
Settlements and curtailments |  | 1 | 0 | 1
Net periodic benefit (credit) cost |  | (25) | 44 | 20
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | 931 | 159 | 784
Prior service (credit) cost |  | 0 | 0 | 0
Settlements and curtailments |  | (1) | 0 | (1)
Amortization of net actuarial loss |  | (111) | (160) | (111)
Amortization of prior service credit (cost) |  | (1) | (2) | (3)
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ 818 | $ (3) | $ 669
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  |  | 4.40% |
Expected long-term rate of return on plan assets (percentage) |  | 8.75% | 8.75% | 8.75%
Weighted average rate of increase for compensation (percentage) |  | 4.22% | 4.22% | 4.21%
Pension Benefits | Minimum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  | 2.87% |  | 5.20%
Pension Benefits | Maximum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  | 4.99% |  | 5.30%
Pension Benefits | Dominion Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost |  | $ 13 | $ 15 | $ 12
Interest cost |  | 30 | 27 | 28
Expected return on plan assets |  | (134) | (126) | (115)
Amortization of prior service (credit) cost |  | 0 | 1 | 1
Amortization of net actuarial loss |  | 13 | 20 | 19
Net periodic benefit (credit) cost |  | (78) | (63) | (55)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | 91 | 97 | 43
Prior service (credit) cost |  | 0 | 0 | 0
Amortization of net actuarial loss |  | (13) | (20) | (19)
Amortization of prior service credit (cost) |  | 0 | (1) | (1)
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ 78 | $ 76 | $ 23
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  | 4.99% | 4.40% | 5.20%
Expected long-term rate of return on plan assets (percentage) |  | 8.75% | 8.75% | 8.75%
Weighted average rate of increase for compensation (percentage) |  | 3.93% | 3.93% | 3.93%
Other Postretirement Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost |  | $ 31 | $ 40 | $ 32
Interest cost |  | 65 | 67 | 67
Expected return on plan assets |  | (118) | (117) | (111)
Amortization of prior service (credit) cost |  | (35) | (27) | (28)
Amortization of net actuarial loss |  | 8 | 6 | 2
Settlements and curtailments |  | 0 | 0 | 0
Net periodic benefit (credit) cost |  | (49) | (31) | (38)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | 178 | (18) | 183
Prior service (credit) cost |  | (216) | (31) | 9
Settlements and curtailments |  | 0 | 0 | 0
Amortization of net actuarial loss |  | (8) | (6) | (2)
Amortization of prior service credit (cost) |  | 35 | 27 | 28
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ (11) | $ (28) | $ 218
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  |  | 4.40% |
Expected long-term rate of return on plan assets (percentage) |  | 8.50% | 8.50% | 8.50%
Weighted average rate of increase for compensation (percentage) |  | 4.22% | 4.22% | 4.22%
Healthcare cost trend rate (percentage) | [1] | 7.00% | 7.00% | 7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (percentage) | [1] | 5.00% | 5.00% | 5.00%
Year that the rate reaches the ultimate trend rate (percentage) | [1],[2] | 2020 | 2019 | 2018
Other Postretirement Plans | Minimum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  | 3.56% |  | 4.20%
Other Postretirement Plans | Maximum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  | 4.94% |  | 5.10%
Other Postretirement Plans | Dominion Gas Holdings, LLC |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost |  | $ 5 | $ 7 | $ 6
Interest cost |  | 14 | 14 | 13
Expected return on plan assets |  | (23) | (24) | (23)
Amortization of prior service (credit) cost |  | 1 | (1) | (1)
Amortization of net actuarial loss |  | 1 | 2 | 0
Net periodic benefit (credit) cost |  | (2) | (2) | (5)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities: |  |  |  |
Current year net actuarial (gain) loss |  | 28 | (9) | 40
Prior service (credit) cost |  | 0 | 0 | 10
Amortization of net actuarial loss |  | (1) | (2) | 0
Amortization of prior service credit (cost) |  | (1) | 1 | 1
Total recognized in other comprehensive income and regulatory assets and liabilities |  | $ 26 | $ (10) | $ 51
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  | 4.93% | 4.40% |
Expected long-term rate of return on plan assets (percentage) |  | 8.50% | 8.50% | 8.50%
Weighted average rate of increase for compensation (percentage) |  | 3.93% | 3.93% | 3.93%
Healthcare cost trend rate (percentage) | [1] | 7.00% | 7.00% | 7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (percentage) | [1] | 5.00% | 5.00% | 5.00%
Year that the rate reaches the ultimate trend rate (percentage) | [1],[2] | 2020 | 2019 | 2018
Other Postretirement Plans | Dominion Gas Holdings, LLC | Minimum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  |  |  | 4.20%
Other Postretirement Plans | Dominion Gas Holdings, LLC | Maximum |  |  |  |
Significant assumptions used to determine periodic cost: |  |  |  |
Discount rate (percentage) |  |  |  | 5.00%
[1] | Assumptions used to determine net periodic cost for the following year.
[2] | The Society of Actuaries model used to determine healthcare cost trend rates was updated in 2014. The new model converges to the ultimate trend rate much more quickly than previous models.

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- Definition Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax + References No definition available. + Details
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- Definition The amount of gains or losses recognized in net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=49177896 + Details
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- Definition An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Expected Long-Term Rate of Return on Plan Assets -URI http://asc.fasb.org/extlink&oid=6512046 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition Expected rate of compensation increases (for pay-related plans). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Expected Return on Plan Assets -URI http://asc.fasb.org/extlink&oid=6512171 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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