Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended	0 Months Ended			3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011 Y	Oct. 18, 2011 Delmarva Power & Light Co/De [Member] Y MW	Jan. 31, 2013 Delmarva Power & Light Co/De [Member] MW	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] MW	Mar. 31, 2012 Atlantic City Electric Co [Member]	Mar. 31, 2012 Wind PPA [Member] Delmarva Power & Light Co/De [Member] MW	Mar. 31, 2011 Wind PPA [Member] Delmarva Power & Light Co/De [Member]	Mar. 31, 2012 Land-Based Wind PPA [Member] Delmarva Power & Light Co/De [Member]	Mar. 31, 2012 Solar PPA [Member] Delmarva Power & Light Co/De [Member] Y MW	Mar. 31, 2012 Non-Utility Generators [Member] Atlantic City Electric Co [Member] MW	Mar. 31, 2011 Non-Utility Generators [Member] Atlantic City Electric Co [Member]	Mar. 31, 2012 Wind Facility One [Member] Wind PPA [Member] Delmarva Power & Light Co/De [Member] MW	Mar. 31, 2012 Wind Facility Two [Member] Wind PPA [Member] Delmarva Power & Light Co/De [Member] MW	Mar. 31, 2012 Wind Facility Three [Member] Wind PPA [Member] Delmarva Power & Light Co/De [Member] MW
Significant Accounting Policies [Line Items]
Number of purchase power agreements							3			3	1
Net power purchases with non-utility generators												$ 51	$ 57
Purchased energy	684	995						9	5		0	50	53
Megawatts received from power purchase agreements (PPAs)								128			10	459
Energy purchase maximum to be purchased, mW														50	40	38
Term of agreement, years			15	21							20
Power of fuel cell facility, mW				30	27	3
Increments to power of fuel cell facility, mW					5
Obligated purchase amount of energy produced at the facility											70.00%
Taxes included in gross revenues	92	96
Increase in revenue and pre-tax earnings		2
Equity ownership percentage							100.00%
Reclassification adjustment relating to uncertain tax positions		$ 1