Employee Benefit Plans (Net Periodic Benefit (Credit) Cost and Amounts Recognized in Other Comprehensive Income and Regulatory Assets and Liabilities) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		$ (691)	$ (648)
Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		(157)	(150)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		118	126	$ 114
Interest cost		317	287	290
Expected return on plan assets		(573)	(531)	(499)
Amortization of prior service (credit) cost		1	2	3
Amortization of net actuarial loss		111	160	111
Settlements and curtailments		1	0	1
Net periodic benefit (credit) cost		(25)	44	20
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		931	159	784
Prior service (credit) cost		0	0	0
Settlements and curtailments		(1)	0	(1)
Amortization of net actuarial loss		(111)	(160)	(111)
Amortization of prior service credit (cost)		(1)	(2)	(3)
Total recognized in other comprehensive income and regulatory assets and liabilities		$ 818	$ (3)	$ 669
Significant assumptions used to determine periodic cost:
Discount rate (percentage)			4.40%
Expected long-term rate of return on plan assets (percentage)		8.75%	8.75%	8.75%
Weighted average rate of increase for compensation (percentage)		4.22%	4.22%	4.21%
Pension Benefits | Minimum
Significant assumptions used to determine periodic cost:
Discount rate (percentage)		2.87%		5.20%
Pension Benefits | Maximum
Significant assumptions used to determine periodic cost:
Discount rate (percentage)		4.99%		5.30%
Pension Benefits | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 13	$ 15	$ 12
Interest cost		30	27	28
Expected return on plan assets		(134)	(126)	(115)
Amortization of prior service (credit) cost		0	1	1
Amortization of net actuarial loss		13	20	19
Net periodic benefit (credit) cost		(78)	(63)	(55)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		91	97	43
Prior service (credit) cost		0	0	0
Amortization of net actuarial loss		(13)	(20)	(19)
Amortization of prior service credit (cost)		0	(1)	(1)
Total recognized in other comprehensive income and regulatory assets and liabilities		$ 78	$ 76	$ 23
Significant assumptions used to determine periodic cost:
Discount rate (percentage)		4.99%	4.40%	5.20%
Expected long-term rate of return on plan assets (percentage)		8.75%	8.75%	8.75%
Weighted average rate of increase for compensation (percentage)		3.93%	3.93%	3.93%
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 31	$ 40	$ 32
Interest cost		65	67	67
Expected return on plan assets		(118)	(117)	(111)
Amortization of prior service (credit) cost		(35)	(27)	(28)
Amortization of net actuarial loss		8	6	2
Settlements and curtailments		0	0	0
Net periodic benefit (credit) cost		(49)	(31)	(38)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		178	(18)	183
Prior service (credit) cost		(216)	(31)	9
Settlements and curtailments		0	0	0
Amortization of net actuarial loss		(8)	(6)	(2)
Amortization of prior service credit (cost)		35	27	28
Total recognized in other comprehensive income and regulatory assets and liabilities		$ (11)	$ (28)	$ 218
Significant assumptions used to determine periodic cost:
Discount rate (percentage)			4.40%
Expected long-term rate of return on plan assets (percentage)		8.50%	8.50%	8.50%
Weighted average rate of increase for compensation (percentage)		4.22%	4.22%	4.22%
Healthcare cost trend rate (percentage)	[1]	7.00%	7.00%	7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (percentage)	[1]	5.00%	5.00%	5.00%
Year that the rate reaches the ultimate trend rate (percentage)	[1],[2]	2020	2019	2018
Other Postretirement Plans | Minimum
Significant assumptions used to determine periodic cost:
Discount rate (percentage)		3.56%		4.20%
Other Postretirement Plans | Maximum
Significant assumptions used to determine periodic cost:
Discount rate (percentage)		4.94%		5.10%
Other Postretirement Plans | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 5	$ 7	$ 6
Interest cost		14	14	13
Expected return on plan assets		(23)	(24)	(23)
Amortization of prior service (credit) cost		1	(1)	(1)
Amortization of net actuarial loss		1	2	0
Net periodic benefit (credit) cost		(2)	(2)	(5)
Changes in plan assets and benefit obligations recognized in other comprehensive income and regulatory assets and liabilities:
Current year net actuarial (gain) loss		28	(9)	40
Prior service (credit) cost		0	0	10
Amortization of net actuarial loss		(1)	(2)	0
Amortization of prior service credit (cost)		(1)	1	1
Total recognized in other comprehensive income and regulatory assets and liabilities		$ 26	$ (10)	$ 51
Significant assumptions used to determine periodic cost:
Discount rate (percentage)		4.93%	4.40%
Expected long-term rate of return on plan assets (percentage)		8.50%	8.50%	8.50%
Weighted average rate of increase for compensation (percentage)		3.93%	3.93%	3.93%
Healthcare cost trend rate (percentage)	[1]	7.00%	7.00%	7.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (percentage)	[1]	5.00%	5.00%	5.00%
Year that the rate reaches the ultimate trend rate (percentage)	[1],[2]	2020	2019	2018
Other Postretirement Plans | Dominion Gas Holdings, LLC | Minimum
Significant assumptions used to determine periodic cost:
Discount rate (percentage)				4.20%
Other Postretirement Plans | Dominion Gas Holdings, LLC | Maximum
Significant assumptions used to determine periodic cost:
Discount rate (percentage)				5.00%

[1] Assumptions used to determine net periodic cost for the following year.

[2] The Society of Actuaries model used to determine healthcare cost trend rates was updated in 2014. The new model converges to the ultimate trend rate much more quickly than previous models.