Income Taxes (Schedule of Deferred Income Taxes) (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred income taxes:
Total deferred income tax assets	$ 1,015	$ 1,101
Total deferred income tax liabilities	1,974	1,941
Total net deferred income tax liabilities	959	840
Depreciation method and plant basis differences	1,139	1,098
Excess deferred income taxes	(228)	(233)
Unrecovered nuclear plant cost	508	529
DESC rate refund	(113)	(140)
Toshiba settlement	(189)	(204)
Nuclear decommissioning	(54)	(51)
Deferred state income taxes	226	208
Federal benefit of deferred state income taxes	(47)	(44)
Deferred fuel, purchased energy and gas costs	27	(12)
Pension benefits	35	39
Other postretirement benefits	(35)	(37)
Loss and credit carryforwards	(343)	(382)
Other	33	69
Deferred Investment Tax Credits-Regulated Operations	16	18
Total Deferred Taxes and Deferred Investment Tax Credits	$ 975	$ 858