Investments (Selected Information Regarding Marketable Equity and Debt Securities) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Available-for-sale securities:
Proceeds from sales		$ 341	$ 243	$ 709	$ 580
Realized gains	[1]	37	44	62	100
Realized losses	[1]	15	12	34	29
Virginia Electric and Power Company
Available-for-sale securities:
Proceeds from sales		154	76	347	209
Realized gains	[2]	18	19	30	37
Realized losses	[2]	$ 7	$ 4	$ 17	$ 15

[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.