Significant Accounting Policies (Schedule of Supplemental Cash Flow Information) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Significant noncash investing and financing activities:
Accrued capital expenditures		$ 341	$ 343
Leases	[1]	9	17
Financing leases		2	17
Virginia Electric and Power Company
Significant noncash investing and financing activities:
Accrued capital expenditures		262	210
Financing leases		$ 1	$ 10

[1] Includes $2 million and $17 million of financing leases at March 31, 2021 and 2020, respectively, and $7 million of operating leases at March 31, 2021.