Significant Accounting Policies (Depreciation Rates and Estimated Useful Life) (Detail)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nonregulated Generation-Nuclear
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives		44 years
Nonregulated Generation-Other | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives		15 years
Nonregulated Generation-Other | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives		30 years
General and Other | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful lives		5 years
General and Other | Maximum
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)	[1]	2.51%	2.84%	2.71%
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)		2.52%	2.94%	2.71%
Transmission
Public Utility, Property, Plant and Equipment [Line Items]
Average composite depreciation rates on utility property, plant and equipment (percentage)	[1]	2.48%	2.50%	2.50%
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%	2.52%
Distribution
Public Utility, Property, Plant and Equipment [Line Items]
Average composite depreciation rates on utility property, plant and equipment (percentage)	[1]	2.76%	2.80%	2.97%
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)		3.19%	3.14%	3.31%
Storage
Public Utility, Property, Plant and Equipment [Line Items]
Average composite depreciation rates on utility property, plant and equipment (percentage)	[1]	1.59%	1.49%	2.20%
General and Other
Public Utility, Property, Plant and Equipment [Line Items]
Average composite depreciation rates on utility property, plant and equipment (percentage)	[1]	4.35%	3.99%	4.11%
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)		5.09%	4.40%	4.52%

[1] Excludes rates for depreciation reported as discontinued operations.