Employee Benefit Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 35	$ 30	$ 104	$ 87
Interest cost	86	79	259	234
Expected return on plan assets	(160)	(141)	(480)	(419)
Amortization of prior service cost (credit)	0	0	1	1
Amortization of net actuarial loss	40	29	121	84
Settlements	1	0	2	0
Net periodic benefit cost (credit)	2	(3)	7	(13)
Pension Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	11	10
Interest cost	7	7	22	22
Expected return on plan assets	(34)	(33)	(105)	(100)
Amortization of prior service cost (credit)	0	0	0	0
Amortization of net actuarial loss	4	3	12	10
Net periodic benefit cost (credit)	(20)	(20)	(60)	(58)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	7	20	23
Interest cost	15	16	45	50
Expected return on plan assets	(32)	(28)	(95)	(87)
Amortization of prior service cost (credit)	(13)	(9)	(38)	(23)
Amortization of net actuarial loss	3	2	9	5
Settlements	0	0	0	0
Net periodic benefit cost (credit)	(20)	(12)	(59)	(32)
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	3	4
Interest cost	3	3	9	10
Expected return on plan assets	(7)	(5)	(19)	(17)
Amortization of prior service cost (credit)	(1)	0	(2)	0
Amortization of net actuarial loss	1	0	2	1
Net periodic benefit cost (credit)	$ (3)	$ (1)	$ (7)	$ (2)