Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 134
Due after one year through five years	379
Due after five years through ten years	403
Due after ten years	416
Total	1,332
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	41
Due after one year through five years	161
Due after five years through ten years	232
Due after ten years	184
Total	$ 618