Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments Owned Federal Income Tax Note [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	21.00%	35.00%
Increase in net operating loss utilization		$ 79
Weighted average rate used to originate deferred tax liability		35.00%
Deferred income taxes, net		$ (379)	$ (184)	$ (780)
Regulatory liabilities		265	(360)	899
Income tax reconciliation, tax reform remeasurement				1
Income tax reconciliation tax reform remeasurement of additional impairment charges.			176
Income tax reconciliation tax reform remeasurement of additional adjustments to deferred income taxes.			23
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	$ (10)	$ 31	$ 13
Income tax examination, description		The statute is closed for IRS examination of years prior to 2010, except for certain outstanding refund claims. The IRS has completed examinations of DESC’s federal returns through 2012. The IRS is currently examining DESC’s federal returns from 2013 through 2017. With few exceptions, DESC is no longer subject to state and local income tax examinations by tax authorities for years prior to 2012
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 65	$ 65
Maximum [Member]
Investments Owned Federal Income Tax Note [Line Items]
Potential increase in earnings in next twelve months if tax benefits recognized		4
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