Discontinued Operations - (Loss) Income from Discontinued Operations, Net of Income Taxes (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended							12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Discontinued Operations [Line Items]
(Loss) Income from Discontinued Operations, net of Income Taxes	$ 8	$ (11)	$ (319)	$ 9	$ 25	$ 15	$ 18	$ (322)	$ 67	$ 35
Cross-Border Energy Lease Investments [Member]
Schedule of Discontinued Operations [Line Items]
(Loss) Income from Discontinued Operations, net of Income Taxes								(327)	41	36
Retail Electric and Natural Gas Supply Businesses of Pepco Energy Services [Member]
Schedule of Discontinued Operations [Line Items]
(Loss) Income from Discontinued Operations, net of Income Taxes								5	26	2
Conectiv Energy [Member]
Schedule of Discontinued Operations [Line Items]
(Loss) Income from Discontinued Operations, net of Income Taxes								$ 0	$ 0	$ (3)