Employee Benefit Plans and Equity Compensation Plan (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, accumulated benefit obligation	$ 579,000,000	$ 578,000,000
Defined benefit plan, annual rate of increase in the per capita cost of covered health care benefits	7.00%
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
Pension and other postretirement benefits	115,000,000	114,000,000
Defined contribution plan, employer matching contributions	$ 14,000,000	13,000,000	$ 11,000,000
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	$ 19,000,000	21,000,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial gain (loss)	(1,000,000)	105,000,000
Defined benefit plan loss due to decrease in discount rate	10,000,000
Defined benefit plan, actuarial gain (loss) in discount rate offset	9,000,000
Actuarial (gain) loss	$ 1,000,000	$ (105,000,000)
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, expected contributions in 2024	$ 8,000,000
Defined benefit plan, net periodic benefit (credit) cost	19,000,000	$ (19,000,000)	$ (13,000,000)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan loss due to decrease in discount rate	(4,000,000)
Defined benefit plan, actuarial gain (loss) in discount rate offset	3,000,000
Actuarial (gain) loss	$ 1,000,000	$ (44,000,000)
Defined benefit plan, ultimate health care cost trend rate	5.00%	5.00%	5.00%
Defined benefit plan, net periodic benefit (credit) cost	$ 5,000,000	$ 7,000,000	$ 7,000,000
Other Postretirement Benefits [Member] | Summer [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, shared costs deferred with joint ownership	10,000,000	9,000,000
Dominion Energy Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, contributions by employer	0	1,000,000	0
Defined benefit plan, net periodic benefit (credit) cost	2,000,000	1,000,000	$ 3,000,000
Pension and other postretirement benefits	$ 6,000,000	$ 4,000,000