Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Due in one year or less	$ 108
Due after one year through five years	281
Due after five years through ten years	359
Due after ten years	382
Total	1,130
Virginia Electric and Power Company
Due in one year or less	19
Due after one year through five years	145
Due after five years through ten years	213
Due after ten years	170
Total	$ 547