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		9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Level 3 Commodity Transactions	Sep. 30, 2012 Level 3 Commodity Transactions Fair Value, Measurements, Recurring	Sep. 30, 2011 Level 3 Commodity Transactions Fair Value, Measurements, Recurring	Sep. 30, 2012 Level 3 Commodity Transactions Fair Value, Measurements, Recurring	Sep. 30, 2011 Level 3 Commodity Transactions Fair Value, Measurements, Recurring	Jun. 30, 2012 Level 3 Virginia Electric and Power Company Commodity Transactions Fair Value, Measurements, Recurring	Jun. 30, 2011 Level 3 Virginia Electric and Power Company Commodity Transactions Fair Value, Measurements, Recurring	Jun. 30, 2012 Level 3 Virginia Electric and Power Company Commodity Transactions Fair Value, Measurements, Recurring	Jun. 30, 2011 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					$ 103	$ 155	$ (122)	$ (71)	$ (50)	$ 1	$ (18)	$ (28)	$ 14
Total realized and unrealized gains (losses):
Included in earnings	(8)	(16)	(31)	(24)		(8)	(16)	(31)	(24)	2	(8)	(44)	(16)
Included in other comprehensive income (loss)						(48)	75	124	16
Included in regulatory assets/liabilities						2	(3)	30	(35)	2	(3)	31	(35)
Settlements						3	24	54	47	(2)	8	44	16
Transfers out of Level 3						(1)	0	(3)	4
Ending balance					103	103	(42)	103	(42)	3	(21)	3	(21)
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	$ (15)	$ 7	$ 25	$ 29		$ (15)	$ 7	$ 25	$ 29