Regulatory Assets and Liabilities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Regulatory Assets And Liabilities [Line Items]
Regulatory assets represented past expenditures not earning return	$ 319
Period expenditures expected to be recovered (years)	2 years
Virginia Electric and Power Company
Regulatory Assets And Liabilities [Line Items]
Regulatory assets represented past expenditures not earning return	$ 240