Significant Financing Transactions - (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended				1 Months Ended
	Sep. 30, 2012 Convertible Debt	Sep. 30, 2011 Convertible Debt	Sep. 30, 2012 Convertible Debt Minimum	Sep. 30, 2012 Convertible Debt Maximum	Feb. 28, 2012 September 2006 hybrids	Jun. 30, 2012 September 2006 hybrids	Mar. 31, 2012 September 2006 hybrids	Sep. 30, 2012 Virginia Electric and Power Company	Jan. 31, 2012 Virginia Electric and Power Company	Sep. 30, 2012 Senior Notes of 1.40% due in 2017	Sep. 30, 2012 Senior Notes of 2.75% due in 2022	Sep. 30, 2012 Senior Notes of 4.05% due in 2042
Credit facility								$ 120
Senior Notes									450	350	350	350
Senior notes interest rates (percentage)									2.95%	1.40%	2.75%	4.05%
Contingent convertible senior notes	82
Conversion rate, shares of common stock per $1,000 principal amount of senior notes (in shares)	29.2650
Principal amount of senior notes	$ 1,000
Conversion rate, shares of common stock per $1,000 principal amount of senior notes, conversion price	$ 34.17
Average Trading Price Principal Amount Of Senior Notes (percentage)	120.00%
Minimum consecutive trading days (days)		20 days	20 days
Maximum consecutive trading days (days)		30 days		30 days
Debt conversion converted instrument amount	61
Tender offer to purchase hybrid subordinated notes					150
Purchased and cancelled of junior subordinated notes						$ 2	$ 86