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
	Mar. 31, 2013	Mar. 31, 2012
Total realized and unrealized gains (losses):
Included in earnings	$ 14	$ (35)
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	(5)	1
Level 3 | Commodity Transactions | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	25	(71)
Total realized and unrealized gains (losses):
Included in earnings	14	(35)
Included in other comprehensive income (loss)	9	5
Included in regulatory assets/liabilities	(5)	11
Settlements	(26)	30
Transfers out of Level 3	(8)	(1)
Ending balance	9	(61)
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	(5)	1
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	(28)
Total realized and unrealized gains (losses):
Included in earnings	2	(27)
Included in regulatory assets/liabilities	(5)	11
Settlements	(2)	27
Ending balance	$ (3)	$ (17)