Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 108
Due after one year through five years	415
Due after five years through ten years	402
Due after ten years	451
Total	1,376
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	19
Due after one year through five years	193
Due after five years through ten years	231
Due after ten years	198
Total	$ 641