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Income Taxes (Narrative) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Jun. 30, 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 $ 18 51    
Increase in goodwill   58    
Unrecognized Tax Benefits,   $ 106