Acquisitions and Dispositions (Schedule of Acquisitions of Solar Projects) (Detail) $ in Millions		1 Months Ended											12 Months Ended
		Oct. 31, 2017 USD ($) Project MW	Sep. 30, 2017 USD ($) Project MW	Jun. 30, 2017 USD ($) Project MW	May 31, 2017 USD ($) Project MW	Mar. 31, 2017 USD ($) Project MW	Feb. 28, 2017 USD ($) Project MW	Nov. 30, 2015 USD ($) Project MW	Jul. 31, 2015 USD ($) Project MW	Jun. 30, 2015 USD ($) Project MW	Apr. 30, 2015 USD ($) Project MW		Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Project Cost													$ 405	$ 40	$ 418
EC&R NA Solar PV, LLC
Business Acquisition [Line Items]
Number of Projects | Project								1			1
Total consideration	[1]							$ 65			$ 66
Project Cost	[2]							$ 65			$ 66
MW Capacity | MW								20			20
EDF Renewable Development, Inc.
Business Acquisition [Line Items]
Number of Projects | Project										1	3	[3]
Total consideration	[1]									$ 68	$ 106	[3]
Project Cost	[2]									$ 68	$ 106	[3]
MW Capacity | MW										18	24	[3]
Sun Peak Solar LLC
Business Acquisition [Line Items]
Number of Projects | Project									1
Total consideration	[1]								$ 42
Project Cost	[2]								$ 71
MW Capacity | MW									20
Community Energy Solar, Inc
Business Acquisition [Line Items]
Number of Projects | Project							1	1
Total consideration	[1]						$ 29	$ 34
Project Cost	[2]						$ 205	$ 212
MW Capacity | MW							100	80
Solar Frontier Americas Holding, LLC
Business Acquisition [Line Items]
Number of Projects | Project	[4]					1
Total consideration	[1]					$ 77
Project Cost	[2]					$ 78
MW Capacity | MW						30
Solar Projects from Cypress Creek Renewables, LLC
Business Acquisition [Line Items]
Number of Projects | Project					1
Total consideration	[1]				$ 154
Project Cost	[2]				$ 160
MW Capacity | MW					79
Hecate Energy Virginia C&C LLC
Business Acquisition [Line Items]
Number of Projects | Project			1	1
Total consideration	[1]		$ 40	$ 16
Project Cost	[2]		$ 41	$ 16
MW Capacity | MW			20	10
Strata Solar Development, LLC/Moorings Farm 2 Holdco, LLC
Business Acquisition [Line Items]
Number of Projects | Project				2
Total consideration	[1]			$ 20
Project Cost	[2]			$ 20
MW Capacity | MW				10
Strata Solar Development, LLC
Business Acquisition [Line Items]
Number of Projects | Project		2
Total consideration	[1]	$ 20
Project Cost	[2]	$ 21
MW Capacity | MW		10

[1] The purchase price was primarily allocated to Property, Plant and Equipment.

[2] Includes acquisition cost.

[3] One of the projects, Marin Carport, began commercial operations in 2016.

[4] In April 2017, Dominion Energy discontinued efforts on the acquisition of the additional 20 MW solar project from Solar Frontier Americas Holding LLC.