Employee Benefit Plans (AOCI and regulatory assets and liabilities that have not been recognized as components of periodic benefit (credit) cost) (Parenthetical) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	$ 3,189	$ 3,204
Amount included in AOCI		1,900	1,900
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	(157)	(136)
Amount included in AOCI		(87)	(103)
Dominion Energy Gas Holdings, LLC | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[2]	367	458
Amount included in AOCI		134	167
Dominion Energy Gas Holdings, LLC | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[2]	$ 24	$ 67

[1] As of December 31, 2017, of the $3.2 billion and $(157) million related to pension benefits and other postretirement benefits, $1.9 billion and $(87) million, respectively, are included in AOCI, with the remainder included in regulatory assets and liabilities. As of December 31, 2016, of the $3.2 billion and $(136) million related to pension benefits and other postretirement benefits, $1.9 billion and $(103) million, respectively, are included in AOCI, with the remainder included in regulatory assets and liabilities.

[2] As of December 31, 2017, of the $367 million related to pension benefits, $134 million is included in AOCI, with the remainder included in regulatory assets and liabilities; the $24 million related to other postretirement benefits is included entirely in regulatory assets and liabilities. As of December 31, 2016, of the $458 million related to pension benefits, $167 million is included in AOCI, with the remainder included in regulatory assets and liabilities; the $67 million related to other postretirement benefits is included entirely in regulatory assets and liabilities.