Employee Benefit Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 30	$ 32	$ 87	$ 95
Interest cost	79	71	234	215
Expected return on plan assets	(141)	(132)	(419)	(398)
Amortization of prior service cost (credit)	0	0	1	1
Amortization of net actuarial loss	29	40	84	120
Net periodic benefit cost (credit)	(3)	11	(13)	33
Pension Benefits | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	4	10	11
Interest cost	7	7	22	21
Expected return on plan assets	(33)	(31)	(100)	(94)
Amortization of net actuarial loss	3	5	10	15
Net periodic benefit cost (credit)	(20)	(15)	(58)	(47)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	10	23	30
Interest cost	16	17	50	50
Expected return on plan assets	(28)	(29)	(87)	(88)
Amortization of prior service cost (credit)	(9)	(7)	(23)	(20)
Amortization of net actuarial loss	2	1	5	4
Net periodic benefit cost (credit)	(12)	(8)	(32)	(24)
Other Postretirement Benefits | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	2	4	5
Interest cost	3	3	10	10
Expected return on plan assets	(5)	(6)	(17)	(18)
Amortization of net actuarial loss	0	1	1	2
Net periodic benefit cost (credit)	$ (1)	$ 0	$ (2)	$ (1)