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Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Significant Accounting Policies [Line Items] |  |  |  |
Accrued unbilled revenue |  | $ 661 | $ 631 |
Percentage of fuel currently subject to deferred fuel accounting |  | 84.00% |  |
Federal statutory income tax rate |  | 35.00% | 35.00% | 35.00%
Recognized interest income |  | $ 11 |  |
Margin deposit assets |  | 92 | $ 82 |
Capitalized interest costs and AFUDC |  | 236 | 159 | $ 100
Unrealized gains reclassified from AOCI to retained earnings |  | 1,100 |  |
Unrealized gains reclassified from AOCI to retained earnings after-tax |  | 734 |  |
Net unrealized gains on equity securities previously classified as cost method investments |  | 36 |  |
Net unrealized gains on equity securities previously classified as cost method investments, after tax |  | 22 |  |
Net unrealized gains in other income |  | 275 |  |
Net unrealized gains in other income, after tax |  | 176 |  |
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings |  | 165 |  |
Change in Estimated Useful Life | Merchant generation assets |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Increase (decrease) in depreciation expense |  | 26 |  |
Increase (decrease) in depreciation expense, after tax |  | $ 16 |  |
NRG Energy, Inc | Four Brothers and Three Cedars | Disposal Group, Disposed of by Sale, Not Discontinued Operations |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Percentage of equity interest sold to noncontrolling interest owners |  | 33.00% |  |
Virginia Electric and Power Company |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Accrued unbilled revenue |  | $ 400 | $ 349 |
Federal statutory income tax rate |  | 35.00% | 35.00% | 35.00%
Recognized interest income |  | $ 11 |  |
Noncurrent income taxes receivable |  | 1 |  |
Margin deposit assets |  | 23 | $ 2 |
Capitalized interest costs |  | 37 | 21 | $ 30
AFUDC related to projects |  | 22 | 31 | $ 19
Unrealized gains reclassified from AOCI to retained earnings |  | 119 |  |
Unrealized gains reclassified from AOCI to retained earnings after-tax |  | 73 |  |
Net unrealized gains on equity securities previously classified as cost method investments |  | 36 |  |
Net unrealized gains on equity securities previously classified as cost method investments, after tax |  | 22 |  |
Net unrealized gains in other income |  | 30 |  |
Net unrealized gains in other income, after tax |  | 19 |  |
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings |  | 13 |  |
Virginia Electric and Power Company | Change in Depreciation Rates from New Depreciation Study |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Increase (decrease) in depreciation expense |  | 40 |  |
Increase (decrease) in depreciation expense, after tax |  | 25 |  |
Virginia Electric and Power Company | Federal |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Noncurrent income taxes receivable |  | 1 |  |
Noncurrent income tax payable |  |  | 2 |
Virginia Electric and Power Company | State |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Noncurrent income taxes receivable |  |  | 13 |
Income tax receivable |  |  | 6 |
Virginia Electric and Power Company | Affiliated Entity |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Income tax payable |  | 16 |  |
Income tax receivable |  |  | 112 |
Virginia Electric and Power Company | Affiliated Entity | Federal |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Income tax payable |  | 16 |  |
Income tax receivable |  |  | 122 |
Virginia Electric and Power Company | Affiliated Entity | State |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Affiliated payables for estimated income taxes owed |  |  | 10 |
Dominion Energy Gas Holdings, LLC |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Accrued unbilled revenue |  | $ 121 | $ 134 |
Federal statutory income tax rate |  | 35.00% | 35.00% | 35.00%
Capitalized interest costs |  | $ 25 | $ 8 | $ 1
Inventory under LIFO method |  | 9 | 13 |
Amount exceeded on LIFO basis |  | 79 | 55 |
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings |  | 26 |  |
Dominion Energy Gas Holdings, LLC | Federal |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Noncurrent income tax payable |  |  | 1 |
Dominion Energy Gas Holdings, LLC | State |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Noncurrent income taxes receivable |  | 14 |  |
Income tax receivable |  |  | 1 |
Noncurrent income tax payable |  |  | 7 |
Dominion Energy Gas Holdings, LLC | Affiliated Entity |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Income tax payable |  | 25 |  |
Income tax receivable |  |  | 11 |
Dominion Energy Gas Holdings, LLC | Affiliated Entity | Federal |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Income tax payable |  | 21 |  |
Income tax receivable |  |  | 10 |
Dominion Energy Gas Holdings, LLC | Affiliated Entity | State |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Income tax payable |  | 4 |  |
Income tax receivable |  |  | $ 1 |
Scenario, Forecast |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Federal statutory income tax rate | 21.00% |  |  |
Retained Earnings |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments |  | 4 |  |
Retained Earnings | Virginia Electric and Power Company |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments |  | 4 |  |
Accounting Standards Update 2017-05 [Member] | Cumulative Effect Of Changes In Accounting Principle [Member] |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Change in accounting principle to reclassify from noncontrolling interests |  | 127 |  |
Current Regulatory Liabilities [Member] |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments |  | 32 |  |
Current Regulatory Liabilities [Member] | Virginia Electric and Power Company |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments |  | $ 32 |  |
Maximum | Nonutility Gas Gathering and Processing |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated Useful Lives |  | 50 years |  |
Maximum | Virginia Electric and Power Company | State |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Noncurrent income taxes receivable |  | $ 1 |  |
Maximum | Dominion Energy Gas Holdings, LLC | Nonutility Gas Gathering and Processing |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated Useful Lives |  | 50 years |  |
Minimum | Nonutility Gas Gathering and Processing |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated Useful Lives |  | 3 years |  |
Minimum | Dominion Energy Gas Holdings, LLC | Nonutility Gas Gathering and Processing |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated Useful Lives |  | 10 years |  |

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