Acquisitions and Dispositions (Schedule of Preliminary Allocation of Purchase Price to Assets Acquired and Liabilities Assumed) (Parenthetical) (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Cash, restricted cash and equivalents		$ 269	$ 391	$ 185	$ 322
Pension and other postretirement benefit liability		2,366	2,328
Impairment of assets and other charges		$ 1,535	$ 403	$ 15
Intangible assets, estimated weighted-average amortization period		10 years
SCANA
Business Acquisition [Line Items]
Equity method investment		$ 31
Cash, restricted cash and equivalents		389
Restricted cash		115
Income tax regulatory assets		258
Pension and other postretirement benefit liability		379
Stock based compensation awards estimated fair value		$ 21
Repayment of letter of credit advances	$ 40
Repayments of Commercial Paper	$ 173
Intangible assets, estimated weighted-average amortization period		5 years
SCANA | Minimum
Business Acquisition [Line Items]
Property, plant and equipment, estimated useful lives		5 years
SCANA | Maximum
Business Acquisition [Line Items]
Property, plant and equipment, estimated useful lives		78 years
SCANA | Dominion Energy | Property plant and equipment committed to forgo recovery
Business Acquisition [Line Items]
Property, plant and equipment with NND project		$ 105
Impairment of assets and other charges		105
Asset impairment charges, after tax		$ 79