Income Taxes - Other Taxes (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery	$ 133	$ 135	$ 145
Property	77	75	71
County Fuel and Energy	153	160	170
Environmental, Use and Other	65	62	65
Total	428	432	451
Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery	108	106	109
Property	45	46	44
County Fuel and Energy	153	160	170
Environmental, Use and Other	62	60	59
Total	368	372	382
Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery	15	14	15
Property	24	21	19
Environmental, Use and Other	1	1	3
Total	40	36	37
Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery	10	14	20
Property	3	3	3
Environmental, Use and Other	1	1	2
Total	$ 14	$ 18	$ 25