Leases (Summary of Total Lease Cost) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Finance lease cost:
Finance lease cost, Amortization	$ 33	$ 20
Finance lease cost, Interest		4
Operating lease cost	68	79
Short-term lease cost	20	26
Variable lease cost	8	5
Total lease cost	129	134
Virginia Electric and Power Company
Finance lease cost:
Operating lease cost	36	41
Short-term lease cost	12	13
Variable lease cost	4	2
Total lease cost	$ 52	$ 56

Amount of interest expense on finance lease liability.

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Amount of amortization expense attributable to right-of-use asset from finance lease.

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Amount of lease cost recognized by lessee for lease contract.

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Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability.

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Amount of short-term lease cost, excluding expense for lease with term of one month or less.

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Amount of variable lease cost, excluded from lease liability, recognized when obligation for payment is incurred for finance and operating leases.

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