Income Taxes (Unrecognized Tax Benefits) (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Contingency [Line Items]
Acquired unrecognized tax benefits			$ 129
Increases-prior period positions	$ 48	$ 18
Decreases in prior period position	$ 59	$ 19
SCANA
Income Tax Contingency [Line Items]
Acquired unrecognized tax benefits			106
Increases-prior period positions			76
Decreases in prior period position			$ 53