Employee Benefit Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 35	$ 29
Interest cost	86	77
Expected return on plan assets	(159)	(139)
Amortization of prior service credit	0	0
Amortization of net actuarial loss	40	28
Settlements	1	0
Net periodic benefit cost (credit)	3	(5)
Pension Benefits | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3
Interest cost	7	8
Expected return on plan assets	(35)	(33)
Amortization of net actuarial loss	4	3
Net periodic benefit cost (credit)	(20)	(19)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	8
Interest cost	16	17
Expected return on plan assets	(32)	(29)
Amortization of prior service credit	(12)	(7)
Amortization of net actuarial loss	3	1
Settlements	0	0
Net periodic benefit cost (credit)	(18)	(10)
Other Postretirement Benefits | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	3	3
Expected return on plan assets	(6)	(5)
Amortization of net actuarial loss	1	0
Net periodic benefit cost (credit)	$ (1)	$ (1)