Investments (Selected Information Regarding Marketable Equity and Debt Securities) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Available-for-sale securities:
Proceeds from sales		$ 300	$ 357	$ 1,009	$ 937
Realized gains	[1]	40	65	102	165
Realized losses	[1]	9	40	43	69
Virginia Electric and Power Company
Available-for-sale securities:
Proceeds from sales		131	198	478	407
Realized gains	[2]	18	45	48	82
Realized losses	[2]	$ 4	$ 18	$ 21	$ 33

[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.