Employee Benefit Plans (Net Periodic Benefit (Credit) Cost and Amounts Recognized in Other Comprehensive Income and Regulatory Assets and Liabilities) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Service cost		$ 162	$ 157	$ 138
Interest cost		394	337	345
Expected return on plan assets		(708)	(663)	(639)
Amortization of prior service (credit) cost		1	1	1
Amortization of net actuarial loss		172	193	162
Settlements and curtailments		72	0	0
Net periodic benefit (credit) cost		93	25	7
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		16	490	142
Prior service (credit) cost		0	0	5
Settlements and curtailments		6	0	1
Amortization of net actuarial loss		(172)	(193)	(162)
Amortization of prior service credit (cost)		(1)	(1)	(1)
Total recognized in other comprehensive income and regulatory assets and liabilities		$ (151)	$ 296	$ (15)
Significant assumptions used to determine periodic cost:
Expected long-term rate of return on plan assets			8.75%	8.75%
Weighted average rate of increase for compensation		4.20%	4.09%	4.09%
Pension Benefits | Dominion Energy Gas Holdings, LLC
Service cost		$ 6	$ 18	$ 15
Interest cost		11	29	30
Expected return on plan assets		(54)	(150)	(141)
Amortization of prior service (credit) cost		0	0	0
Amortization of net actuarial loss		7	19	16
Settlements and curtailments		1
Net periodic benefit (credit) cost		(29)	(84)	(80)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		(46)	207	(75)
Prior service (credit) cost		0	0	0
Amortization of net actuarial loss		(7)	(19)	(16)
Amortization of prior service credit (cost)		0	0	0
Total recognized in other comprehensive income and regulatory assets and liabilities		$ (53)	$ 188	$ (91)
Significant assumptions used to determine periodic cost:
Discount rate			3.81%	4.50%
Expected long-term rate of return on plan assets		8.65%	8.75%	8.75%
Weighted average rate of increase for compensation		4.55%	4.11%	4.11%
Pension Benefits | Minimum
Significant assumptions used to determine periodic cost:
Discount rate		3.57%	3.80%	3.31%
Expected long-term rate of return on plan assets		7.00%
Pension Benefits | Minimum | Dominion Energy Gas Holdings, LLC
Significant assumptions used to determine periodic cost:
Discount rate		4.10%
Pension Benefits | Maximum
Significant assumptions used to determine periodic cost:
Discount rate		4.43%	3.81%	4.50%
Expected long-term rate of return on plan assets		8.65%
Pension Benefits | Maximum | Dominion Energy Gas Holdings, LLC
Significant assumptions used to determine periodic cost:
Discount rate		4.42%
Other Postretirement Benefits
Service cost		$ 26	$ 27	$ 26
Interest cost		68	56	60
Expected return on plan assets		(140)	(143)	(128)
Amortization of prior service (credit) cost		(52)	(52)	(51)
Amortization of net actuarial loss		10	11	13
Settlements and curtailments		42	0	0
Net periodic benefit (credit) cost		(46)	(101)	(80)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		(98)	78	12
Prior service (credit) cost		2	(4)	(73)
Settlements and curtailments		0	0	2
Amortization of net actuarial loss		(10)	(11)	(13)
Amortization of prior service credit (cost)		52	52	51
Total recognized in other comprehensive income and regulatory assets and liabilities		$ (54)	$ 115	$ (21)
Significant assumptions used to determine periodic cost:
Discount rate			3.76%
Expected long-term rate of return on plan assets		8.50%	8.50%	8.50%
Healthcare cost trend rate	[1]		7.00%	7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	[1]	5.00%	5.00%	5.00%
Year that the rate reaches the ultimate trend rate	[1]		2022	2021
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC
Service cost		$ 1	$ 4	$ 4
Interest cost		5	11	12
Expected return on plan assets		(16)	(28)	(24)
Amortization of prior service (credit) cost		(5)	(4)	(3)
Amortization of net actuarial loss		3	3	2
Settlements and curtailments		1
Net periodic benefit (credit) cost		(11)	(14)	(9)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		(21)	16	18
Prior service (credit) cost		0	(4)	(61)
Amortization of net actuarial loss		(3)	(3)	(2)
Amortization of prior service credit (cost)		5	4	3
Total recognized in other comprehensive income and regulatory assets and liabilities		$ (19)	$ 13	$ (42)
Significant assumptions used to determine periodic cost:
Discount rate			3.81%	4.47%
Expected long-term rate of return on plan assets		8.50%	8.50%	8.50%
Healthcare cost trend rate	[1]	6.50%	7.00%	7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	[1]	5.00%	5.00%	5.00%
Year that the rate reaches the ultimate trend rate	[1]	2025	2022	2021
Other Postretirement Benefits | Minimum
Significant assumptions used to determine periodic cost:
Discount rate		4.05%		3.92%
Healthcare cost trend rate	[1]	6.50%
Year that the rate reaches the ultimate trend rate	[1]	2023
Other Postretirement Benefits | Minimum | Dominion Energy Gas Holdings, LLC
Significant assumptions used to determine periodic cost:
Discount rate		4.05%
Other Postretirement Benefits | Maximum
Significant assumptions used to determine periodic cost:
Discount rate		4.41%		4.47%
Healthcare cost trend rate	[1]	6.60%
Year that the rate reaches the ultimate trend rate	[1]	2025
Other Postretirement Benefits | Maximum | Dominion Energy Gas Holdings, LLC
Significant assumptions used to determine periodic cost:
Discount rate		4.37%

[1] Assumptions used to determine net periodic cost for the following year.