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Significant Accounting Policies (Depreciation Rates and Estimated Useful Life) (Detail) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Merchant Generation Nuclear |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 44 years |  |
LNG Facility [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 40 years |  |
Minimum | Merchant Generation-Other |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 15 years |  |
Minimum | Nonutility Gas Gathering and Processing |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 3 years |  |
Minimum | Nonutility Gas Gathering and Processing | Dominion Energy Gas Holdings, LLC |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 10 years |  |
Minimum | General and Other |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 5 years |  |
Maximum | Merchant Generation-Other |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 30 years |  |
Maximum | Nonutility Gas Gathering and Processing |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 50 years |  |
Maximum | Nonutility Gas Gathering and Processing | Dominion Energy Gas Holdings, LLC |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 50 years |  |
Maximum | General and Other |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Estimated useful lives | 59 years |  |
Generation |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.71% | 2.94% | 2.83%
Generation | Virginia Electric and Power Company |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.71% | 2.94% | 2.83%
Transmission |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.54% | 2.55% | 2.47%
Transmission | Virginia Electric and Power Company |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.52% | 2.54% | 2.36%
Transmission | Dominion Energy Gas Holdings, LLC |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.45% | 2.40% | 2.43%
Distribution |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.97% | 3.00% | 3.02%
Distribution | Virginia Electric and Power Company |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 3.31% | 3.32% | 3.32%
Storage |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.40% | 2.48% | 2.29%
Storage | Dominion Energy Gas Holdings, LLC |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.46% | 2.45% | 2.19%
Gas Gathering and Processing |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.62% | 2.21% | 2.66%
Gas Gathering and Processing | Dominion Energy Gas Holdings, LLC |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 3.07% | 2.42% | 2.58%
General and Other |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 4.56% | 4.89% | 4.12%
General and Other | Virginia Electric and Power Company |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 4.52% | 4.68% | 3.49%
General and Other | Dominion Energy Gas Holdings, LLC |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 5.59% | 4.96% | 4.54%
Distribution | Dominion Energy Gas Holdings, LLC |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average composite depreciation rates on utility property, plant and equipment (percentage) | 2.41% | 2.42% | 2.55%

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