Fair Value Measurements (Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category) (Details) - Commodity - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 152	$ 124	$ 139	$ 95
Total realized and unrealized gains (losses):
Included in earnings	(11)	(7)	(36)	(23)
Included in other comprehensive income	0	0	0	2
Included in regulatory assets/liabilities	11	(37)	34	(5)
Settlements	1	9	13	27
Transfers out of Level 3	0	0	3	(7)
Ending balance	153	89	153	89
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets/liabilities still held at the reporting date	1	0	1	0
Virginia Electric and Power Company
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	152	125	143	93
Total realized and unrealized gains (losses):
Included in earnings	(12)	(7)	(37)	(24)
Included in regulatory assets/liabilities	11	(37)	34	(5)
Settlements	1	7	12	24
Ending balance	152	88	152	88
Dominion Energy Gas Holdings, LLC
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance			(2)	6
Total realized and unrealized gains (losses):
Included in other comprehensive income			(1)	2
Transfers out of Level 3			3	(8)
Ending balance	$ 0	$ 0	$ 0	$ 0