Significant Accounting Policies (Narrative) (Detail) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2018 USD ($) Contract $ / shares	Mar. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
Payments for sales and services due period		1 month
Cash provided by other investing activities		$ 4	$ 4
Operating Revenue	[1]	3,466	3,384
Other energy-related purchases		744	575
Purchased gas		340	305
Unrealized gains reclassified from AOCI to retained earnings		1,100
Unrealized gains reclassified from AOCI to retained earnings after-tax		734
Unrealized gain (loss) on securities recorded in other income, before tax	[2]	$ (84)
Loss per share from unrealized lLoss on securities | $ / shares		$ 0.06
Other operations and maintenance		$ 796	784
Other income		100	162
Tax reform, reclassification of tax expense (benefit) from AOCI to retained earnings		(289)
Accounting Standards Update 2014-09 [Member] | Performing Processing And Fractionation Services
Significant Accounting Policies [Line Items]
Operating Revenue		25	0
Other energy-related purchases		25	0
Accounting Standards Update 2014-09 [Member] | Transportation And Storage Arrangements
Significant Accounting Policies [Line Items]
Operating Revenue			(32)
Purchased gas			(32)
Accounting Standards Update 2016-01 [Member]
Significant Accounting Policies [Line Items]
Unrealized gain (loss) on securities recorded in other income, before tax		(47)
Unrealized gain (loss) on securities recorded in other income, net of tax		(38)
Cumulative Effect Of Changes In Accounting Principle [Member] | Accounting Standards Update 2014-09 [Member]
Significant Accounting Policies [Line Items]
Change in accounting principle to retained earnings and membership interest		3
Cumulative Effect Of Changes In Accounting Principle [Member] | Accounting Standards Update201705
Significant Accounting Policies [Line Items]
Change in accounting principle to retained earnings and membership interest		$ 127
Previously Reported
Significant Accounting Policies [Line Items]
Cash provided by other investing activities			11
Other operations and maintenance			738
Other income			116
Merchant Solar Projects | Terra Nova Renewable Partners
Significant Accounting Policies [Line Items]
Percentage of equity interest sold to noncontrolling interest owners		33.00%
Merchant Solar Projects | Terra Nova Renewable Partners | Call Option
Significant Accounting Policies [Line Items]
Percentage ownership in total units		67.00%
Four Brothers and Three Cedars
Significant Accounting Policies [Line Items]
Percentage ownership in total units		50.00%
Dominion Energy Midstream Partners, LP | Common and Subordinated Units
Significant Accounting Policies [Line Items]
Ownership interest percentage of limited partner interests		50.50%
Dominion Energy Midstream Partners, LP | Convertible Preferred Interests
Significant Accounting Policies [Line Items]
Ownership interest percentage of limited partner interests		37.50%
NRG Energy, Inc | Four Brothers and Three Cedars
Significant Accounting Policies [Line Items]
Percentage of equity interest sold to noncontrolling interest owners		33.00%
Virginia Electric and Power Company
Significant Accounting Policies [Line Items]
Cash provided by other investing activities		$ (6)	(3)
Operating Revenue	[3]	1,748	1,831
Other energy-related purchases	[3]	591	456
Unrealized gains reclassified from AOCI to retained earnings		119
Unrealized gains reclassified from AOCI to retained earnings after-tax		73
Net unrealized gains on equity securities previously classified as cost method investments		36
Net unrealized gains on equity securities previously classified as cost method investments, after tax		22
Unrealized gain (loss) on securities recorded in other income, before tax	[2]	(47)
Other income		3	31
Tax reform, reclassification of tax expense (benefit) from AOCI to membership interests		3
Virginia Electric and Power Company | Retained Earnings
Significant Accounting Policies [Line Items]
Net unrealized gains on equity securities previously classified as cost method investments		3
Virginia Electric and Power Company | Current Regulatory Liabilities [Member]
Significant Accounting Policies [Line Items]
Net unrealized gains on equity securities previously classified as cost method investments		33
Virginia Electric and Power Company | Accounting Standards Update 2016-01 [Member]
Significant Accounting Policies [Line Items]
Unrealized gain (loss) on securities recorded in other income, before tax		(8)
Unrealized gain (loss) on securities recorded in other income, net of tax		(6)
Virginia Electric and Power Company | Previously Reported
Significant Accounting Policies [Line Items]
Cash provided by other investing activities			0
Dominion Energy Gas Holdings, LLC
Significant Accounting Policies [Line Items]
Cash provided by other investing activities		(5)	(8)
Operating Revenue	[4]	526	490
Purchased gas	[4]	29	43
Other income		33	25
Tax reform, reclassification of tax expense (benefit) from AOCI to membership interests		(26)
Dominion Energy Gas Holdings, LLC | Accounting Standards Update 2014-09 [Member] | Performing Processing And Fractionation Services
Significant Accounting Policies [Line Items]
Operating Revenue		25	0
Other energy-related purchases		25	0
Dominion Energy Gas Holdings, LLC | Accounting Standards Update 2014-09 [Member] | Transportation And Storage Arrangements
Significant Accounting Policies [Line Items]
Operating Revenue			(24)
Purchased gas			(24)
Dominion Energy Gas Holdings, LLC | Cumulative Effect Of Changes In Accounting Principle [Member] | Accounting Standards Update 2014-09 [Member]
Significant Accounting Policies [Line Items]
Change in accounting principle to retained earnings and membership interest		$ 3
Dominion Energy Gas Holdings, LLC | Previously Reported
Significant Accounting Policies [Line Items]
Cash provided by other investing activities			0
Other operations and maintenance			133
Other income			$ 5
DETI | Cumulative Effect Of Changes In Accounting Principle [Member]
Significant Accounting Policies [Line Items]
Number of existing contracts | Contract		3

[1] See Note 10 for amounts attributable to related parties.

[2] Included in other income and the nuclear decommissioning trust regulatory liability as discussed in Note 2.

[3] See Note 18 for amounts attributable to affiliates.

[4] See Note 18 for amounts attributable to related parties.