Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments Owned Federal Income Tax Note [Line Items]
Increase in net operating loss utilization				$ 79
Weighted average rate used to originate deferred tax liability		35.00%
Increase Decrease in Income Tax Expense		$ 38
Deferred income taxes, net		117	$ 229	(379)
Regulatory liabilities		(109)	(193)	265
Increase in income tax expense	$ 1
Increase in unrecognized tax benefits	53
Reduction in credit carryforward deferred tax assets	(45)
Increase in accrued taxes	$ 7	$ 7	$ (3)	(10)
Income tax examination, description		The statute is closed for IRS examination of years prior to 2013. The IRS is currently examining DESC’s federal returns from 2013 through 2017. DESC is no longer subject to state and local income tax examinations by tax authorities for years prior to 2018
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 13
Maximum [Member]
Investments Owned Federal Income Tax Note [Line Items]
Potential increase in earnings in next twelve months if tax benefits recognized		$ 1
Prior to SCANA Combination
Investments Owned Federal Income Tax Note [Line Items]
Increase in unrecognized tax benefits				79
Increase in income tax expense				67
Earliest Tax Year | Federal | IRS
Investments Owned Federal Income Tax Note [Line Items]
Income tax examination, year under examination		2013
Latest Tax Year | Federal | IRS
Investments Owned Federal Income Tax Note [Line Items]
Income tax examination, year under examination		2017
SCANA Combination
Investments Owned Federal Income Tax Note [Line Items]
Deferred income taxes, net				194
Increase in deferred income tax expense				30
Regulatory liabilities				40
Increase in deferred tax assets				$ 10