Employee Benefit Plans (Net Periodic Benefit Cost (Credit)) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 39	$ 35
Interest cost		84	86
Expected return on plan assets		(165)	(159)
Amortization of prior service credit		0	0
Amortization of net actuarial loss		48	40
Settlements		0	1
Net periodic benefit cost (credit)	[1]	6	3
Pension Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost		4	4
Interest cost		7	7
Expected return on plan assets		(37)	(35)
Amortization of prior service credit		0	0
Amortization of net actuarial loss		5	4
Net periodic benefit cost (credit)	[2]	(21)	(20)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		7	7
Interest cost		14	16
Expected return on plan assets		(36)	(32)
Amortization of prior service credit		(13)	(12)
Amortization of net actuarial loss		3	3
Settlements		0	0
Net periodic benefit cost (credit)	[1]	(25)	(18)
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost		1	1
Interest cost		3	3
Expected return on plan assets		(8)	(6)
Amortization of prior service credit		(1)	0
Amortization of net actuarial loss		1	1
Net periodic benefit cost (credit)	[2]	$ (4)	$ (1)

[1] The components of net periodic benefit cost (credit) other than the service cost component are included in other income in the Consolidated Statements of Income.

[2] The components of net periodic benefit credit other than the service cost component are included in other income in the Consolidated Statements of Income.