Employee Benefit Plans (Components of AOCI and Regulatory Assets and Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss		$ (25)
Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss		$ (3)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 161
Prior service (credit) cost	1
Pension Benefits | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	16
Prior service (credit) cost	0
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	13
Prior service (credit) cost	(47)
Other Postretirement Plans | Dominion Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	2
Prior service (credit) cost	$ 1