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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 130	$ 109	$ 139	$ 95
Total realized and unrealized gains (losses):
Included in earnings	(10)	(10)	(25)	(17)
Included in other comprehensive income	0	0	0	3
Included in regulatory assets/liabilities	32	15	23	32
Settlements	0	10	12	18
Transfers out of Level 3	0	0	3	(7)
Ending balance	152	124	152	124
Virginia Electric and Power Company
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	132	110	143	93
Total realized and unrealized gains (losses):
Included in earnings	(10)	(9)	(25)	(17)
Included in regulatory assets/liabilities	31	15	23	32
Settlements	(1)	9	11	17
Ending balance	152	125	152	125
Dominion Energy Gas Holdings, LLC
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	0	0	(2)	6
Total realized and unrealized gains (losses):
Included in other comprehensive income	0	0	(1)	2
Transfers out of Level 3	0	0	3	(8)
Ending balance	$ 0	$ 0	$ 0	$ 0