Investments (Fair Value of our Marketable Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less	$ 169
Due after one year through five years	390
Due after five years through ten years	426
Due after ten years	483
Total	1,468
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less	40
Due after one year through five years	180
Due after five years through ten years	242
Due after ten years	219
Total	$ 681