Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Effective Income Tax Computation [Line Items]
Federal statutory income tax rate	21.00%	21.00%	35.00%
Percentage of deductibility of interest expense	30.00%
SCANA
Effective Income Tax Computation [Line Items]
Deferred income tax expense	$ 198
Increase in unrecognized tax benefits	51
Increase in goodwill	40
Unrecognized Tax Benefits,	$ 106

Effective income tax computation.

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Effective income tax rate reconciliation deductions interest expense percent.

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Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase in unrecognized tax benefits resulting from acquisitions.

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Amount of increase (decrease) in unrecognized tax benefits attributable to uncertain tax positions taken in tax returns.

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