Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Due in one year or less	$ 162
Due after one year through five years	333
Due after five years through ten years	367
Due after ten years	415
Total	1,277
Virginia Electric and Power Company
Due in one year or less	44
Due after one year through five years	160
Due after five years through ten years	202
Due after ten years	165
Total	$ 571