Leases (Weighted Average Remaining Lease Term and Weighted Discounted Rate for Finance and Operating Leases) (Detail)	Dec. 31, 2020	Dec. 31, 2019
Lessee Lease Disclosure [Line Items]
Weighted average remaining lease term - finance leases	5 years	5 years
Weighted average remaining lease term - operating leases	26 years	22 years
Weighted average discount rate - finance leases	3.17%	3.83%
Weighted average discount rate - operating leases	4.07%	4.48%
Virginia Electric and Power Company
Lessee Lease Disclosure [Line Items]
Weighted average remaining lease term - finance leases	6 years	6 years
Weighted average remaining lease term - operating leases	21 years	20 years
Weighted average discount rate - finance leases	2.51%	4.12%
Weighted average discount rate - operating leases	4.26%	4.29%