Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	$ 233
Due after one year through five years	383
Due after five years through ten years	435
Due after ten years	505
Total	1,556
Virginia Electric and Power Company
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less	51
Due after one year through five years	168
Due after five years through ten years	245
Due after ten years	240
Total	$ 704