Employee Benefit Plans (Summary of Changes in Pension and Other Postretirement Benefit Plans) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in fair value of plan assets:
Actual return (loss) on plan assets			$ 534	$ (72)
Dominion Gas Holdings, LLC
Changes in fair value of plan assets:
Actual return (loss) on plan assets			130	(13)
Pension Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year			6,391	6,667
Dominion Questar Combination			817	0
Service cost			118	126	$ 114
Interest cost			317	287	290
Benefits paid			(286)	(246)
Actuarial (gains) losses during the year			784	(443)
Plan amendments	[1]		0	0
Settlements and curtailments	[2]		(9)	0
Benefit obligation at end of year			8,132	6,391	6,667
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year			6,166	6,480
Dominion Questar Combination			704	0
Actual return (loss) on plan assets			426	(71)
Employer contributions			15	3
Benefits paid			(286)	(246)
Settlements	[2]		(9)	0
Fair value of plan assets at end of year			7,016	6,166	6,480
Funded status at end of year			(1,116)	(225)
Noncurrent pension and other postretirement benefit assets			930	931
Other current liabilities			(43)	(14)
Noncurrent pension and other postretirement benefit liabilities			(2,003)	(1,142)
Net amount recognized			$ (1,116)	$ (225)
Weighted average rate of increase for compensation (percentage)			4.09%	4.22%
Pension Benefits | Minimum
Changes in fair value of plan assets:
Discount percentage rate			3.31%	4.96%
Pension Benefits | Maximum
Changes in fair value of plan assets:
Discount percentage rate			4.50%	4.99%
Pension Benefits | Dominion Gas Holdings, LLC
Changes in benefit obligation:
Benefit obligation at beginning of year			$ 608	$ 638
Service cost			13	15	12
Interest cost			30	27	28
Benefits paid			(32)	(29)
Actuarial (gains) losses during the year			64	(43)
Benefit obligation at end of year			683	608	638
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year			1,467	1,510
Actual return (loss) on plan assets			107	(14)
Employer contributions			0	0
Benefits paid			(32)	(29)
Fair value of plan assets at end of year			1,542	1,467	1,510
Funded status at end of year			859	859
Noncurrent pension and other postretirement benefit assets			859	859
Noncurrent pension and other postretirement benefit liabilities	[3]		0	0
Net amount recognized			$ 859	$ 859
Discount percentage rate			4.50%	4.99%
Weighted average rate of increase for compensation (percentage)			4.11%	3.93%
Other Postretirement Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year			$ 1,430	$ 1,571
Dominion Questar Combination			85	0
Service cost			31	40	32
Interest cost			65	67	67
Benefits paid			(83)	(79)
Actuarial (gains) losses during the year			166	(138)
Plan amendments	[1]		(216)	(31)
Settlements and curtailments	[2]		0	0
Benefit obligation at end of year			1,478	1,430	1,571
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year			1,382	1,402
Dominion Questar Combination			45	0
Actual return (loss) on plan assets			108	(1)
Employer contributions			12	12
Benefits paid			(35)	(31)
Settlements	[2]		0	0
Fair value of plan assets at end of year			1,512	1,382	1,402
Funded status at end of year			34	(48)
Noncurrent pension and other postretirement benefit assets			148	12
Other current liabilities			(5)	(3)
Noncurrent pension and other postretirement benefit liabilities			(109)	(57)
Net amount recognized			$ 34	$ (48)
Weighted average rate of increase for compensation (percentage)			3.29%	4.22%
Other Postretirement Benefits | Minimum
Changes in fair value of plan assets:
Discount percentage rate			3.92%	4.93%
Other Postretirement Benefits | Maximum
Changes in fair value of plan assets:
Discount percentage rate			4.47%	4.94%
Other Postretirement Benefits | Dominion Gas Holdings, LLC
Changes in benefit obligation:
Benefit obligation at beginning of year			$ 292	$ 320
Service cost			5	7	6
Interest cost			14	14	13
Benefits paid			(19)	(18)
Actuarial (gains) losses during the year			28	(31)
Benefit obligation at end of year			320	292	320
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year			283	288
Actual return (loss) on plan assets			23	1
Employer contributions			12	12
Benefits paid			(19)	(18)
Fair value of plan assets at end of year			299	283	$ 288
Funded status at end of year			(21)	(9)
Noncurrent pension and other postretirement benefit assets			0	0
Noncurrent pension and other postretirement benefit liabilities	[3]		(21)	(9)
Net amount recognized			$ (21)	$ (9)
Discount percentage rate			4.47%	4.93%
Weighted average rate of increase for compensation (percentage)				3.93%
Retiree medical coverage
Changes in fair value of plan assets:
Discount percentage rate		3.71%
Retirement age		65 years

[1] 2016 amount relates primarily to a plan amendment that changed post-65 retiree medical coverage for certain current and future Local 50 retirees effective April 1, 2017. 2015 amount relates primarily to a plan amendment that changed retiree medical benefits for certain nonunion employees after Medicare eligibility.

[2] Relates primarily to a settlement for certain executives.

[3] Reflected in other deferred credits and other liabilities in Dominion Gas' Consolidated Balance Sheets.