Leases (Weighted Average Remaining Lease Term and Weighted Discounted Rate for Finance and Operating Leases) (Detail)	Dec. 31, 2021	Dec. 31, 2020
Lessee Lease Disclosure [Line Items]
Weighted average remaining lease term - finance leases	5 years	5 years
Weighted average remaining lease term - operating leases	27 years	26 years
Weighted average discount rate - finance leases	2.77%	3.17%
Weighted average discount rate - operating leases	3.96%	4.07%
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	25 years	21 years
Weighted average discount rate - finance leases	2.27%	2.51%
Weighted average discount rate - operating leases	4.00%	4.26%