Commitment and Contingencies (Schedule of Long Term Purchase Commitments) (Details) - Virginia Electric and Power Company - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Long-term Purchase Commitment [Line Items]
Present value of total commitment for capacity payments		$ 347
Purchased electric capacity
Long-term Purchase Commitment [Line Items]
2017	[1]	149
2018	[1]	93
2019	[1]	60
2020	[1]	52
2021	[1]	46
Thereafter	[1]	0
Total	[1]	400
Payments		248	$ 305	$ 330
Energy payments
Long-term Purchase Commitment [Line Items]
Payments		$ 126	$ 198	$ 304

[1] Commitments represent estimated amounts payable for capacity under power purchase contracts with qualifying facilities and independent power producers, the last of which ends in 2021. Capacity payments under the contracts are generally based on fixed dollar amounts per month, subject to escalation using broad-based economic indices. At December 31, 2016, the present value of Virginia Power's total commitment for capacity payments is $347 million. Capacity payments totaled $248 million, $305 million, and $330 million, and energy payments totaled $126 million, $198 million, and $304 million for the years ended 2016, 2015 and 2014, respectively.