Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended					12 Months Ended				3 Months Ended	12 Months Ended																12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Dec. 31, 2011 years	Dec. 31, 2010 employees	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2011 Delmarva Power & Light Co/De [Member]	Dec. 31, 2010 Delmarva Power & Light Co/De [Member]	Dec. 31, 2009 Delmarva Power & Light Co/De [Member]	Oct. 18, 2011 Delmarva Power & Light Co/De [Member]	Sep. 30, 2011 Atlantic City Electric Co [Member]	Dec. 31, 2011 Atlantic City Electric Co [Member]	Dec. 31, 2010 Atlantic City Electric Co [Member]	Dec. 31, 2009 Atlantic City Electric Co [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member]	Dec. 31, 2010 Potomac Electric Power Co [Member]	Dec. 31, 2009 Potomac Electric Power Co [Member]	Dec. 31, 2011 Wind PPA [Member] Delmarva Power & Light Co/De [Member] mW	Dec. 31, 2010 Wind PPA [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Land-Based Wind PPA [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Solar PPA [Member] Delmarva Power & Light Co/De [Member] mW years	Dec. 31, 2011 Non-Utility Generators [Member] Atlantic City Electric Co [Member] mW	Dec. 31, 2010 Non-Utility Generators [Member] Atlantic City Electric Co [Member]	Dec. 31, 2009 Non-Utility Generators [Member] Atlantic City Electric Co [Member]	Dec. 31, 2011 Hurricane Irene [Member]	Dec. 31, 2011 Asset Removal Costs [Member]	Dec. 31, 2010 Asset Removal Costs [Member]	Dec. 31, 2011 Wind Facility One [Member] Wind PPA [Member] Delmarva Power & Light Co/De [Member] mW	Dec. 31, 2011 Wind Facility Two [Member] Wind PPA [Member] Delmarva Power & Light Co/De [Member] mW	Dec. 31, 2011 Wind Facility Three [Member] Wind PPA [Member] Delmarva Power & Light Co/De [Member] mW
Significant Accounting Policies [Line Items]
Regulatory Liabilities		$ 528	$ 526	$ 528																							$ 388	$ 361
Net power purchases with non-utility generators																							218	292	282
Purchased energy			3,422	4,631	5,330														18	12		1	206	270	262
Incremental storm costs			6									8														43
Other operation and maintenance			914	884	819			239	255	238			226	204	190	420	354	328								28
Capital expenditures																										15
Eliminated positions				164
Number of purchase power agreements													3								3	1
Megawatts received from power purchase agreements (PPAs)																			128			10	459
Energy purchase maximum to be purchased, mW																													50.00	40	38
AFUDC for borrowed funds			11	8	7
Term of agreement, years			15																			20
Awards received from the U.S. DOE				149										19
AFUDC for equity component			15	10	3
Unbilled revenue		218	179	218
Power of fuel cell facility, mW											30
Proceeds from contract termination			2
Obligated purchase amount of energy produced at the facility																						70.00%
Taxes included in gross revenues			390	373	293
Increase in revenue and pre-tax earnings			2
Other operation and maintenance expense																										6
Regulatory assets		1,915	2,196	1,915																						22
Reclassification adjustment								11									5
Equity ownership percentage													100.00%
Preferred stock, shares authorized		40,000,000	40,000,000	40,000,000
Preferred stock, shares outstanding		0	0	0										62,145.00
Preferred stock, par value		$ 0.01	$ 0.01	$ 0.01
Income tax (expense) benefit after-tax		15	28	21	12			42	31	16			33	43	17	36	37	76
Additional income tax (expense) benefit after-tax	17		(3)
Reclassification adjustment relating to continuing operations				(5)
Reclassification adjustment relating to uncertain tax positions			2
Reclassification adjustment analysis of deferred income tax balances					6
Asset retirement obligation accrual		4
Asset retirement obligation amounts that should have been recorded in period					$ 1	$ 1	$ 1