Fair Value Measurements (Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Total realized and unrealized gains (losses):
Included in earnings	$ (10)		$ 12	$ 2	$ (23)
The amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets/liabilities still held at the reporting date	(4)		33	(11)	33
Level 3 | Commodity Transactions | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	9	25	(61)	25	(71)
Total realized and unrealized gains (losses):
Included in earnings	(10)		12	2	(23)
Included in other comprehensive income (loss)	26		166	36	171
Included in regulatory assets/liabilities	(22)		18	(27)	29
Settlements	(1)		21	(26)	51
Transfers out of Level 3	0		(1)	(8)	(2)
Ending balance	2	9	155	2	155
The amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets/liabilities still held at the reporting date		(4)	33	(11)	33
Level 3 | Virginia Electric and Power Company | Commodity Transactions | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		2	(17)	2	(28)
Total realized and unrealized gains (losses):
Included in earnings		(7)	(19)	(4)	(46)
Included in regulatory assets/liabilities		(22)	18	(27)	29
Settlements		7	19	4	46
Ending balance	$ (25)	$ (3)	$ 1	$ (25)	$ 1