Fair Value Measurements (Net Change in the Assets and Liabilities Measured at Fair Value on a Recurrring Basis and Included in the Level 3 Fair Value Category) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
Included in earnings	$ (15)	$ (77)	$ 43
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets still held at the reporting date	42	22	(4)
Commodity | Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets still held at the reporting date	42	22	(4)
Commodity | Level 3 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
Beginnning balance	(71)	(50)	(66)
Included in earnings	(15)	(77)	43
Included in other comprehensive income (loss)	101	14	(49)
Included in regulatory assets/liabilities	30	(42)	24
Settlements	47	88	(38)
Transfers out of Level 3	67	4	(36)
Ending balance	25	(71)	(50)
Commodity | Virginia Electric and Power Company | Level 3 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
Beginnning balance	(28)	14	(10)
Included in earnings	(50)	(45)	51
Included in regulatory assets/liabilities	30	(42)	24
Settlements	50	45	(51)
Transfers out of Level 3	0	0	0
Ending balance	$ 2	$ (28)	$ 14