Employee Benefit Plans (Summary of Changes in Pension and Other Postretirement Benefit Plans) (Detail) - USD ($) $ in Millions		1 Months Ended		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019
Changes in fair value of plan assets:
Employer contributions					$ 499
Amounts recognized in the Consolidated Balance Sheets at December 31:
Noncurrent pension and other postretirement benefit assets		$ 1,704	$ 1,707	$ 1,704	1,707
Noncurrent pension and other postretirement benefit liabilities		(1,706)	(2,364)	(1,706)	(2,364)
Pension Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year				10,446	8,500
Dominion Energy SCANA Combination					854
Service cost				173	162	$ 157
Interest cost				351	394	337
Benefits paid				(461)	(470)
Actuarial (gains) losses during the year				992	1,054
Settlements, curtailments and special termination benefits	[1]			(138)	(48)
Benefit obligation at end of year		11,363	10,446	11,363	10,446	8,500
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year				9,631	7,197
Dominion Energy SCANA Combination					727
Actual return (loss) on plan assets				1,602	1,747
Employer contributions		250	520	278	557
Benefits paid				(461)	(470)
Settlements	[2]			(71)	(127)
Fair value of plan assets at end of year		10,979	9,631	10,979	9,631	7,197
Funded status at end of year		(384)	(815)	(384)	(815)
Amounts recognized in the Consolidated Balance Sheets at December 31:
Noncurrent pension and other postretirement benefit assets		1,054	1,266	1,054	1,266
Other current liabilities		(14)	(29)	(14)	(29)
Noncurrent pension and other postretirement benefit liabilities		(1,424)	(2,052)	(1,424)	(2,052)
Net amount recognized		$ (384)	$ (815)	$ (384)	$ (815)
Significant assumptions used to determine benefit obligations as of December 31:
Weighted average rate of increase for compensation		4.53%	4.23%	4.53%	4.23%
Pension Benefits | Minimum
Significant assumptions used to determine benefit obligations as of December 31:
Discount rate		2.73%	3.47%	2.73%	3.47%		4.07%
Crediting interest rate for cash balance and similar plans		1.93%	2.67%	1.93%	2.67%
Crediting interest rate for cash balance and similar plans		1.93%	2.67%	1.93%	2.67%
Pension Benefits | Maximum
Significant assumptions used to determine benefit obligations as of December 31:
Discount rate		2.95%	3.63%	2.95%	3.63%		4.10%
Crediting interest rate for cash balance and similar plans		2.15%	2.83%	2.15%	2.83%
Crediting interest rate for cash balance and similar plans		2.15%	2.83%	2.15%	2.83%
Other Postretirement Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year				$ 1,769	$ 1,363
Dominion Energy SCANA Combination					253
Service cost				28	26	27
Interest cost				58	68	56
Benefits paid				(120)	(96)
Actuarial (gains) losses during the year				33	111
Plan amendments				(6)
Settlements, curtailments and special termination benefits	[1]			(16)	44
Benefit obligation at end of year		$ 1,746	$ 1,769	1,746	1,769	1,363
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year				1,880	1,581
Actual return (loss) on plan assets				300	349
Employer contributions				13	12
Benefits paid				(93)	(62)
Fair value of plan assets at end of year		2,100	1,880	2,100	1,880	$ 1,581
Funded status at end of year		354	111	354	111
Amounts recognized in the Consolidated Balance Sheets at December 31:
Noncurrent pension and other postretirement benefit assets		650	442	650	442
Other current liabilities		(15)	(17)	(15)	(17)
Noncurrent pension and other postretirement benefit liabilities		(281)	(314)	(281)	(314)
Net amount recognized		$ 354	$ 111	$ 354	$ 111
Other Postretirement Benefits | Minimum
Significant assumptions used to determine benefit obligations as of December 31:
Discount rate		2.69%	3.44%	2.69%	3.44%		4.05%
Other Postretirement Benefits | Maximum
Significant assumptions used to determine benefit obligations as of December 31:
Discount rate		2.80%	3.52%	2.80%	3.52%		4.08%

[1] 2020 amounts include curtailments and settlements recognized as a result of the GT&S Transaction as well as settlements of qualified and nonqualified pension obligations. 2019 amounts relate primarily to a curtailment and settlement as a result of the voluntary retirement program.

[2] 2020 amounts relate primarily to settlements of qualified and nonqualified pension obligations. 2019 amounts relate primarily to a settlement as a result of the voluntary retirement program.