Investments (Selected Information Regarding Marketable Equity and Debt Securities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Available-for-sale securities:
Proceeds from sales	$ 554		$ 415
Realized gains	63	[1]	28	[1]
Realized losses	6	[1]	4	[1]
Virginia Electric and Power Company
Available-for-sale securities:
Proceeds from sales	189		191
Realized gains	16	[1]	11	[1]
Realized losses	$ 3	[1]	$ 2	[1]

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