Investments (Selected Information Regarding Marketable Equity and Debt Securities) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Available-for-sale securities:
Proceeds from sales		$ 756	$ 368
Realized gains	[1]	94	25
Realized losses	[1]	20	19
Virginia Electric and Power Company
Available-for-sale securities:
Proceeds from sales		330	193
Realized gains	[2]	45	12
Realized losses	[2]	$ 10	$ 10

[1] Includes realized gains and losses recorded to the nuclear decommissioning trust regulatory liability.

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