Employee Benefit Plans and Equity Compensation Plan (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, accumulated benefit obligation	$ 578,000,000	$ 697,000,000
Defined benefit plan, annual rate of increase in the per capita cost of covered health care benefits	6.25%
Defined benefit plan, ultimate health care cost trend rate	5.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets	7.00%
Defined benefit plan, contributions by employer	$ 0	0	$ 0
Amounts due to Dominion	871,000,000	458,000,000
Pension and other postretirement benefits	114,000,000	164,000,000
Defined contribution plan, employer matching contributions	$ 13,000,000	11,000,000	$ 14,000,000
Global Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	45.00%
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	53.00%
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	2.00%
U.S Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	60.00%
Non-U.S Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	40.00%
Summer [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, shared costs deferred with joint ownership	$ 21,000,000	14,000,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial gain (loss)	$ 105,000,000	$ 29,000,000
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets	7.00%	7.00%	7.00%
Defined benefit plan, net periodic benefit (credit) cost	$ (19,000,000)	$ (13,000,000)	$ 4,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial gain (loss)	$ 44,000,000	$ 8,000,000
Defined benefit plan, ultimate health care cost trend rate	5.00%	5.00%	5.00%
Defined benefit plan, net periodic benefit (credit) cost	$ 7,000,000	$ 7,000,000	$ 11,000,000
Other Postretirement Benefits [Member] | Summer [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, shared costs deferred with joint ownership	9,000,000	12,000,000
Dominion Energy Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, contributions by employer	1,000,000	0
Defined benefit plan, net periodic benefit (credit) cost	1,000,000	3,000,000
Pension and other postretirement benefits	$ 4,000,000	$ 3,000,000