Commitments and Contingencies (Nuclear Insurance) (Detail)	Dec. 31, 2019 USD ($)
Millstone
Guarantor Obligations [Line Items]
Property insurance coverage	$ 1,700,000,000
Kewaunee
Guarantor Obligations [Line Items]
Property insurance coverage	50,000,000.00
Summer
Guarantor Obligations [Line Items]
Property insurance coverage	2,750,000,000
Surry | Virginia Electric and Power Company
Guarantor Obligations [Line Items]
Property insurance coverage	1.70
North Anna | Virginia Electric and Power Company
Guarantor Obligations [Line Items]
Property insurance coverage	$ 1.70