Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less	$ 116
Due after one year through five years	304
Due after five years through ten years	357
Due after ten years	369
Total	1,146
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less	18
Due after one year through five years	156
Due after five years through ten years	217
Due after ten years	157
Total	$ 548