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Significant Accounting Policies (Narrative) (Detail) $ / shares in Units, $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 USD ($) Mcfe | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) Mcfe Contract $ / shares | Dec. 31, 2017 USD ($) Mcfe | Dec. 31, 2016 USD ($)
Significant Accounting Policies [Line Items] |  |  |  |  |
Accrued unbilled revenue | $ 626 |  | $ 626 | $ 661 |
Percentage of fuel currently subject to deferred fuel accounting |  |  | 84.00% |  |
Federal statutory income tax rate |  |  | 21.00% | 35.00% | 35.00%
Recognized interest income |  |  | $ 11 | $ 11 |
Income tax payable | 11 |  | 11 |  |
Margin deposit assets | $ 95 |  | 95 | 92 |
Capitalized interest costs and AFUDC |  |  | 134 | 236 | $ 159
Impairment of assets and other charges |  |  | $ 403 | $ 15 | 4
Estimated proved developed or proved gas and oil reserves rate per unit | Mcfe | 1.89 |  | 1.89 | 2.11 |
Operating revenue |  |  |  |  | 7,348
Purchased gas |  |  | $ 645 | $ 701 | $ 459
Unrealized gains reclassified from AOCI to retained earnings | $ 1,100 |  | 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 |  | 36 |  |
Net unrealized gains on equity securities previously classified as cost method investments, after tax | 22 |  | 22 |  |
Net unrealized gains in other income |  |  | 190 |  |
Net unrealized gains in other income, after tax |  |  | $ 142 |  |
Gain per share from unrealized loss on securities | $ / shares |  |  | $ 0.22 |  |
Tax reform, reclassification of tax benefit from AOCI to retained earnings |  |  | $ 289 |  |
Accounting Standards Update 2014-09 [Member] | Cumulative Effect Of Changes In Accounting Principle [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Change in accounting principle to retained earnings and membership interests | 3 |  | 3 |  |
Accounting Standards Update 2017-05 [Member] | Cumulative Effect Of Changes In Accounting Principle [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Change in accounting principle to retained earnings and membership interests | 127 |  | 127 |  |
Current Regulatory Liabilities [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments | 33 |  | 33 |  |
Retained Earnings |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments | 3 |  | 3 |  |
Affiliated Entity |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable | 2 |  | 2 |  |
Maximum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating lease, right-of-use asset | 500 |  | $ 500 |  |
Maximum | Nonutility Gas Gathering and Processing |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives |  |  | 50 years |  |
Minimum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating lease, right-of-use asset | 450 |  | $ 450 |  |
Minimum | Nonutility Gas Gathering and Processing |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives |  |  | 3 years |  |
Change in Depreciation Rates from New Depreciation Study |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Increase (decrease) in EPS | $ / shares |  |  | $ 0.07 |  |
Change in Estimated Useful Life [Member] | Merchant generation assets |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Increase (decrease) in depreciation expense |  |  | $ (30) | 26 |
Increase (decrease) in depreciation expense, after tax |  |  | (23) | 16 |
Performing Processing And Fractionation Services [Member] | Accounting Standards Update 2014-09 [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating revenue |  |  | 107 | 0 |
Other energy-related purchases |  |  | 107 | 0 |
Transportation And Storage Arrangements [Member] | Accounting Standards Update 2014-09 [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating revenue |  |  |  | 111 |
Purchased gas |  |  |  | 111 |
Virginia Electric and Power Company |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Accrued unbilled revenue | 392 |  | $ 392 | $ 400 |
Federal statutory income tax rate |  |  | 21.00% | 35.00% | 35.00%
Recognized interest income |  |  | $ 11 | $ 11 |
Noncurrent income taxes receivable |  |  |  | 1 |
Margin deposit assets | 1 |  | 1 | 23 |
Capitalized interest costs |  |  | 56 | 37 | $ 21
AFUDC related to projects |  |  | 4 | 22 | $ 31
Unrealized gains reclassified from AOCI to retained earnings | 119 |  | 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 |  | 36 |  |
Net unrealized gains on equity securities previously classified as cost method investments, after tax | 22 |  | 22 |  |
Net unrealized gains in other income |  |  | 24 |  |
Net unrealized gains in other income, after tax |  |  | 18 |  |
Tax reform, reclassification of tax benefit from AOCI to retained earnings |  |  | 3 |  |
Virginia Electric and Power Company | Scenario, Forecast |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Impairment of assets and other charges |  | $ 190 |  |  |
Asset Impairment Charges After Tax |  | $ 141 |  |  |
Virginia Electric and Power Company | Current Regulatory Liabilities [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments | 33 |  | 33 |  |
Virginia Electric and Power Company | Retained Earnings |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Net unrealized gains on equity securities previously classified as cost method investments | 3 |  | 3 |  |
Virginia Electric and Power Company | Affiliated Entity |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable | 36 |  | 36 | 16 |
Virginia Electric and Power Company | Change in Depreciation Rates from New Depreciation Study |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Increase (decrease) in depreciation expense |  |  | (60) | 40 |
Increase (decrease) in depreciation expense, after tax |  |  | (44) | 25 |
Virginia Electric and Power Company | Federal |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Noncurrent income taxes receivable |  |  |  | 1 |
Virginia Electric and Power Company | Federal | Affiliated Entity |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable | 34 |  | 34 | 16 |
Virginia Electric and Power Company | State | Affiliated Entity |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable | 2 |  | 2 |  |
Virginia Electric and Power Company | State | Maximum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Noncurrent income taxes receivable |  |  |  | 1 |
Dominion Energy Gas Holdings, LLC |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Accrued unbilled revenue | 101 |  | $ 101 | $ 85 |
Federal statutory income tax rate |  |  | 21.00% | 35.00% | 35.00%
Capitalized interest costs |  |  | $ 25 | $ 34 | $ 13
Impairment of assets and other charges | 219 |  | 163 | 15 |
Inventory under LIFO method | 12 |  | 12 | 9 |
Amount exceeded on LIFO basis | 87 |  | 87 | 79 |
Purchased gas |  |  | (10) | 109 | $ 92
Tax reform, reclassification of tax benefit from AOCI to retained earnings |  |  | 26 |  |
Dominion Energy Gas Holdings, LLC | Affiliated Entity |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable | 271 |  | $ 271 | 52 |
Dominion Energy Gas Holdings, LLC | Nonutility Gas Gathering and Processing |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives |  |  | 40 years |  |
Dominion Energy Gas Holdings, LLC | Maximum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating lease, right-of-use asset | 70 |  | $ 70 |  |
Dominion Energy Gas Holdings, LLC | Minimum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating lease, right-of-use asset | 60 |  | 60 |  |
Dominion Energy Gas Holdings, LLC | Performing Processing And Fractionation Services [Member] | Accounting Standards Update 2014-09 [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Other energy-related purchases |  |  |  | 0 |
Dominion Energy Gas Holdings, LLC | Transportation And Storage Arrangements [Member] | Accounting Standards Update 2014-09 [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating revenue |  |  |  | 71 |
Purchased gas |  |  |  | 71 |
Dominion Energy Gas Holdings, LLC | Federal |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable | 277 |  | 277 |  |
Dominion Energy Gas Holdings, LLC | Federal | Affiliated Entity |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable | 6 |  | 6 | 46 |
Dominion Energy Gas Holdings, LLC | State |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Noncurrent income taxes receivable | 15 |  | $ 15 | 14 |
Dominion Energy Gas Holdings, LLC | State | Affiliated Entity |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Income tax payable |  |  |  | $ 6 |
DETI | Accounting Standards Update 2014-09 [Member] | Cumulative Effect Of Changes In Accounting Principle [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Number of existing contracts | Contract |  |  | 3 |  |
Virginia Power [Member] | Maximum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating lease, right-of-use asset | 250 |  | $ 250 |  |
Virginia Power [Member] | Minimum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Operating lease, right-of-use asset | 200 |  | $ 200 |  |
SCANA | Maximum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives |  |  | 78 years |  |
Capital lease obligation non - current | 35 |  | $ 35 |  |
SCANA | Minimum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives |  |  | 5 years |  |
Capital lease obligation non - current | $ 30 |  | $ 30 |  |
Merchant Solar Projects | Terra Nova Renewable Partners |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Business Acquisition, Percentage of Voting Interests Acquired | 50.00% |  | 50.00% |  |
Merchant Solar Projects | Terra Nova Renewable Partners |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Percentage of equity interest sold to noncontrolling interest owners | 33.00% |  | 33.00% |  |
Merchant Solar Projects | Terra Nova Renewable Partners | Call Option |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Percentage ownership in total units | 67.00% |  | 67.00% |  |

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