Investments (Selected Information Regarding Marketable Equity and Debt Securities) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale securities:
Proceeds from sales		$ 1,422	$ 1,340	$ 1,235
Realized gains	[1]	128	219	171
Realized losses	[1]	55	84	30
Virginia Electric and Power Company
Available-for-sale securities:
Proceeds from sales		733	639	549
Realized gains	[2]	63	110	73
Realized losses	[2]	$ 27	$ 43	$ 12

[1] Includes realized gains and losses recorded to the nuclear decommissioning trust regulatory liability as discussed in Note 2.

[2] Includes realized gains and losses recorded to the nuclear decommissioning trust regulatory liability as discussed in Note 2.