Significant Accounting Policies (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended	6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended				3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended	3 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011 Year	Jun. 30, 2012 Hurricane [Member]	Jun. 30, 2012 Minimum [Member] Hurricane [Member]	Jun. 30, 2012 Maximum [Member] Hurricane [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member]	Jun. 30, 2011 Atlantic City Electric Co [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member]	Jun. 30, 2011 Atlantic City Electric Co [Member]	Dec. 31, 2011 Atlantic City Electric Co [Member] Year	Jun. 30, 2012 Atlantic City Electric Co [Member] Hurricane [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member] Minimum [Member] Hurricane [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member] Maximum [Member] Hurricane [Member]	Jun. 30, 2011 Pepco Energy Services [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member]	Jun. 30, 2011 Potomac Electric Power Co [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member]	Jun. 30, 2011 Potomac Electric Power Co [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member] Hurricane [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member] Minimum [Member] Hurricane [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] Hurricane [Member]	Oct. 31, 2011 Delmarva Power & Light Co/De [Member] Year MW	Jun. 30, 2012 Delmarva Power & Light Co/De [Member]	Jun. 30, 2011 Delmarva Power & Light Co/De [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member]	Jun. 30, 2011 Delmarva Power & Light Co/De [Member]	Jan. 31, 2013 Delmarva Power & Light Co/De [Member] Energy Efficiency Programs [Member] MW	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Energy Efficiency Programs [Member] MW	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Hurricane [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Minimum [Member] Hurricane [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] Hurricane [Member]	Jun. 30, 2012 Pepco Holdings Inc [Member]	Jun. 30, 2011 Pepco Holdings Inc [Member]	Jun. 30, 2011 Pepco Holdings Inc [Member]	Jun. 30, 2011 Phi [Member]	Jun. 30, 2012 Non-Utility Generators [Member] Atlantic City Electric Co [Member]	Jun. 30, 2011 Non-Utility Generators [Member] Atlantic City Electric Co [Member]	Jun. 30, 2012 Non-Utility Generators [Member] Atlantic City Electric Co [Member] MW	Jun. 30, 2011 Non-Utility Generators [Member] Atlantic City Electric Co [Member]	Jun. 30, 2012 Wind Ppa [Member] Delmarva Power & Light Co/De [Member]	Jun. 30, 2011 Wind Ppa [Member] Delmarva Power & Light Co/De [Member]	Jun. 30, 2012 Wind Ppa [Member] Delmarva Power & Light Co/De [Member] MW	Jun. 30, 2011 Wind Ppa [Member] Delmarva Power & Light Co/De [Member]	Jun. 30, 2012 Wind Ppa [Member] Delmarva Power & Light Co/De [Member] Wind Facility One [Member] MW	Jun. 30, 2012 Wind Ppa [Member] Delmarva Power & Light Co/De [Member] Wind Facility Two [Member] MW	Jun. 30, 2012 Wind Ppa [Member] Delmarva Power & Light Co/De [Member] Wind Facility Three [Member] MW	Jun. 30, 2012 Solar Ppa [Member] Delmarva Power & Light Co/De [Member]	Jun. 30, 2012 Solar Ppa [Member] Delmarva Power & Light Co/De [Member] MW Year	Jun. 30, 2012 Land-Based Wind PPA [Member] Delmarva Power & Light Co/De [Member]
Significant Accounting Policies [Line Items]
Incremental storm costs						$ 3,000,000	$ 70,000,000	$ 85,000,000						$ 900,000	$ 29,000,000	$ 35,000,000				$ 9,900,000		$ 1,600,000	$ 39,000,000	$ 47,000,000				$ 4,600,000				$ 500,000	$ 2,000,000	$ 3,000,000
Other operation and maintenance	224,000,000	209,000,000	449,000,000	443,000,000		1,800,000			56,000,000	51,000,000	112,000,000	106,000,000		500,000				101,000,000	100,000,000	204,000,000	202,000,000	1,000,000				62,000,000	47,000,000	127,000,000	112,000,000			300,000
Capital Expenditure						1,200,000								400,000								600,000										200,000
Regulatory assets						1,500,000								500,000								800,000										200,000
Other operation and maintenance expense						300,000																200,000										100,000
Number of purchase power agreements											3																																								1	3
Megawatts received from power purchase agreements (PPAs)																																									459				128						10
Net power purchases with non-utility generators																																							49,000,000	55,000,000	100,000,000	112,000,000
Purchased energy	555,000,000	812,000,000	1,239,000,000	1,811,000,000																																			47,000,000	51,000,000	98,000,000	104,000,000	6,000,000	4,000,000	15,000,000	9,000,000
Energy purchase maximum to be purchased, mW																																															50	40	38
Term of agreement, years					15								15												21																										20
Obligated purchase amount of energy produced at the facility																																																			70.00%
Purchased energy																																																		1,000,000	1,000,000
Power of fuel cell facility, mW																									30					27	3
Increments to power of fuel cell facility, mW																														5
Equity ownership percentage									100.00%		100.00%
Number of Standard Offer Capacity Agreements					3								3
Taxes included in gross revenues	93,000,000	94,000,000	184,000,000	190,000,000					3,000,000	5,000,000	7,000,000	10,000,000						86,000,000	85,000,000	169,000,000	171,000,000					4,000,000	4,000,000	8,000,000	9,000,000
Operating revenue	1,000,000	3,000,000	1,000,000	7,000,000																						1,000,000		1,000,000
Increase in revenue and pre-tax earnings																	2,000,000
Other operation and maintenance expense		(8,000,000)		(8,000,000)																							(8,000,000)		(8,000,000)
Deferred tax Adjustment																																				1,000,000	1,000,000
Increase in income tax expense										1,000,000		1,000,000						1,000,000			1,000,000														1,000,000		1,000,000
Self-insurance reserves reduced										$ 1,000,000									$ 1,000,000								$ 2,000,000											$ 4,000,000