Income Taxes (Schedule of Deferred Income Taxes) (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred income taxes:
Total deferred income tax assets	$ 3,285	$ 3,736
Total deferred income tax liabilities	9,069	9,883
Total net deferred income tax liabilities	5,784	6,147
Plant and equipment, primarily depreciation method and basis differences	5,824	6,616
Excess deferred income taxes	(1,142)	(1,306)
Unrecovered NND Project costs	529	553
DESC rate refund	(140)	(169)
Toshiba Settlement	(204)	(219)
Nuclear decommissioning	991	909
Deferred state income taxes	702	863
Federal benefit of deferred state income taxes	(147)	(184)
Deferred fuel, purchased energy and gas costs	(28)
Deferred fuel, purchased energy and gas costs		30
Pension benefits	239	174
Other postretirement benefits	(14)	(37)
Loss and credit carryforwards	(1,534)	(1,832)
Valuation allowances	155	161
Partnership basis differences	593	823
Other	(40)	(235)
Total net deferred income tax liabilities	5,784	6,147
Deferred Investment Tax Credits – Regulated Operations	169	130
Total Deferred Taxes and Deferred Investment Tax Credits	5,953	6,277
Virginia Electric and Power Company
Deferred income taxes:
Total deferred income tax assets	1,204	1,207
Total deferred income tax liabilities	3,832	4,058
Total net deferred income tax liabilities	2,628	2,851
Plant and equipment, primarily depreciation method and basis differences	3,227	3,359
Excess deferred income taxes	(656)	(672)
Unrecovered NND Project costs	0	0
DESC rate refund	0	0
Toshiba Settlement	0	0
Nuclear decommissioning	303	290
Deferred state income taxes	305	302
Federal benefit of deferred state income taxes	(64)	(63)
Deferred fuel, purchased energy and gas costs	(34)
Deferred fuel, purchased energy and gas costs		1
Pension benefits	(105)	(153)
Other postretirement benefits	76	62
Loss and credit carryforwards	(354)	(280)
Valuation allowances	6	5
Partnership basis differences	0	0
Other	(76)	0
Total net deferred income tax liabilities	2,628	2,851
Deferred Investment Tax Credits – Regulated Operations	151	111
Total Deferred Taxes and Deferred Investment Tax Credits	$ 2,779	$ 2,962