Commitments and Contingencies (Nuclear Insurance) (Detail) $ in Millions	Dec. 31, 2020 USD ($)
Millstone
Guarantee Obligations [Line Items]
Property insurance coverage	$ 1,700
Kewaunee
Guarantee Obligations [Line Items]
Property insurance coverage	50
Summer
Guarantee Obligations [Line Items]
Property insurance coverage	2,750
Surry | Virginia Electric and Power Company
Guarantee Obligations [Line Items]
Property insurance coverage	1,700	[1]
North Anna | Virginia Electric and Power Company
Guarantee Obligations [Line Items]
Property insurance coverage	$ 1,700	[1]

[1] Surry and North Anna share a blanket property limit of $200 million.