Income Taxes (Other Taxes) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Income Tax [Line Items]
Gross Receipts/Delivery	$ 135	$ 145	$ 145
Property	75	71	70
County Fuel and Energy	160	170	154
Environmental, Use and Other	62	65	65
Total	432	451	434
Potomac Electric Power Co [Member]
Schedule Of Income Tax [Line Items]
Gross Receipts/Delivery	106	109	108
Property	46	44	42
County Fuel and Energy	160	170	154
Environmental, Use and Other	60	59	60
Total	372	382	364
Delmarva Power & Light Co/De [Member]
Schedule Of Income Tax [Line Items]
Gross Receipts/Delivery	14	15	16
Property	21	19	19
Environmental, Use and Other	1	3	2
Total	36	37	37
Atlantic City Electric Co [Member]
Schedule Of Income Tax [Line Items]
Gross Receipts/Delivery	14	20	20
Property	3	3	3
Environmental, Use and Other	1	2	3
Total	$ 18	$ 25	$ 26