Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2013 Virginia Electric and Power Company	Mar. 31, 2012 Virginia Electric and Power Company
Net deferred gains (losses) on derivative-hedging activities, tax	$ 54	$ (80)	$ (1)	$ 0
Changes in unrealized net gains (losses) on investment securities, tax	(51)	(56)	(5)	(5)
Net derivative (gains) losses-hedging activities, tax	(48)	12	0	(1)
Net realized (gains) losses on investment securities, tax	18	6	1	1
Net pension and other postretirement benefit costs, tax	$ (9)	$ (9)