Regulatory Matters - Additional Information (Detail) (USD $)	1 Months Ended			12 Months Ended		12 Months Ended	0 Months Ended	1 Months Ended		12 Months Ended			12 Months Ended			1 Months Ended				12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended										12 Months Ended			12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended					12 Months Ended				12 Months Ended		1 Months Ended	12 Months Ended	0 Months Ended	1 Months Ended		12 Months Ended		1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended
	Aug. 31, 2013	May 31, 2013	Dec. 31, 2012 mi	Dec. 31, 2013	Apr. 30, 2012 MW	Dec. 31, 2013 Regulatory Asset [Member]	Dec. 18, 2013 MAPP Abandonment Costs [Member]	May 31, 2013 District of Columbia [Member] DC Undergrounding Task Force [Member]	May 13, 2013 District of Columbia [Member] DC Undergrounding Task Force [Member] Districts	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2011 Minimum [Member]	Apr. 30, 2012 Minimum [Member] MW	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2011 Maximum [Member]	Apr. 30, 2012 Maximum [Member] MW	Mar. 31, 2013 Atlantic City Electric Co [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member]	Feb. 28, 2012 Atlantic City Electric Co [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member]	Jul. 19, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member] New Jersey Settlement [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] New Jersey Settlement [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member] Distribution Rate [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member] Recovery Charges [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Minimum [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Maximum [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 18, 2013 Delmarva Power & Light Co/De [Member]	Oct. 31, 2013 Delmarva Power & Light Co/De [Member]	Oct. 08, 2013 Delmarva Power & Light Co/De [Member]	Oct. 02, 2013 Delmarva Power & Light Co/De [Member]	Aug. 30, 2013 Delmarva Power & Light Co/De [Member]	Aug. 27, 2013 Delmarva Power & Light Co/De [Member]	Aug. 28, 2013 Delmarva Power & Light Co/De [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member]	Mar. 29, 2013 Delmarva Power & Light Co/De [Member]	Mar. 31, 2013 Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member] mi	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] MW	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Regulatory Asset [Member]	Mar. 01, 2015 Delmarva Power & Light Co/De [Member] Scenario, Forecast [Member] Advanced Metering Infrastructure Costs [Member]	May 01, 2014 Delmarva Power & Light Co/De [Member] Scenario, Forecast [Member] Advanced Metering Infrastructure Costs [Member]	Mar. 29, 2013 Delmarva Power & Light Co/De [Member] Expected [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Expected [Member]	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Minimum [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Minimum [Member] MW	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] MW	Mar. 29, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member] Expected [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member] Expected [Member]	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 04, 2013 Potomac Electric Power Co [Member]	Jul. 12, 2013 Potomac Electric Power Co [Member]	May 31, 2013 Potomac Electric Power Co [Member]	Mar. 08, 2013 Potomac Electric Power Co [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member]	Jul. 31, 2012 Potomac Electric Power Co [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member] mi	Dec. 31, 2011 Potomac Electric Power Co [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] MW	Dec. 31, 2013 Potomac Electric Power Co [Member] Regulatory Asset [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member] MAPP Abandonment Costs [Member]	May 13, 2013 Potomac Electric Power Co [Member] District of Columbia [Member] Districts	Dec. 31, 2013 Potomac Electric Power Co [Member] District of Columbia [Member]	Dec. 04, 2013 Potomac Electric Power Co [Member] Expected [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member] Expected [Member]	Jul. 31, 2012 Potomac Electric Power Co [Member] Expected [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member] Expected [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member] Actual [Member]	Feb. 27, 2013 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] Minimum [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] Minimum [Member] MW	Feb. 27, 2013 Potomac Electric Power Co [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] Maximum [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] MW	Nov. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] Expected [Member]	Feb. 27, 2013 Potomac Electric Power Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	May 31, 2013 PHI [Member]
Regulatory Matters [Line Items]
Transition bond maturity, lower range				2014																2014
Transition bond maturity, upper range				2023																2023
Incremental Storm Restoration Costs Amortization and recovery period											3 years			5 years						3 years																							5 years																								5 years
Return on assets						12.80%																																								12.80%																									12.80%
Regulatory asset, amortization period, years										P1Y			P20Y															P1Y		P20Y																							P1Y			P20Y																										P1Y			P20Y
Depreciation reserve, amortization period				8 years 3 months																8 years 3 months
Requested rate change																	$ 70,400,000																		$ 56,000,000					$ 22,800,000	$ 39,000,000	$ 12,000,000																						$ 44,800,000	$ 60,800,000	$ 18,100,000								$ 44,800,000	$ 43,300,000	$ 60,800,000	$ 18,100,000	$ 68,400,000	$ 66,200,000
Return on equity, percentage																	10.25%			10.80%		9.75%	9.75%			8.70%	11.30%		6.78%		10.33%									10.25%	10.25%	10.25%	10.80%								8.70%	11.30%			6.78%					10.33%	10.25%	9.36%		10.25%	10.25%	9.31%	10.80%		10.75%					10.25%						8.70%	11.30%			6.78%				10.33%
Interim rate increase implemented																																							2,500,000
Additional interim rate increase implemented																																	25,100,000	25,100,000
Interim rates in effect subject to refund																																	27,600,000	27,600,000
Increased distribution base period																																			4 years
Estimated rate of equity, year one																																			7.41%
Estimated rate of equity, year two																																			8.80%
Estimated rate of equity, year three																																			9.75%
Estimated rate of equity, year four																																			9.75%
Customer refundable fees																																			500,000
Rate additional increase implemented																																				15,000,000	6,800,000																									27,900,000
Return on equity																																					9.75%																									9.36%
Base rate period																																															2 years	2 years
Portion of advanced metering infrastructure in percentage																																															50.00%	50.00%
Effect of proposed change on gas cost rate	5.50%																																					5.50%
Surcharge for recovery of costs																																																	10,200,000	10,200,000																										192,000,000
Proposed incentive for meeting enhanced reliability goals																																																										500,000	500,000																	1,000,000
Credit to customers																																																										500,000	500,000																												1,000,000
ROE for calculating the AFUDC and regulatory asset carrying costs																																				9.81%
Deferred operation and maintenance expenses																																				6,000,000																										23,600,000
Period of amortized expenses																																				5 years																										5 years
Charges on cost of recovery																																				4,200,000																										24,000,000
Annual depreciation and amortization expenses																																																																		27,300,000	27,300,000
Components of request rate change																								72,100,000	(1,700,000)
Increase in base rate																						25,500,000	25,500,000
Distribution revenue increase																						70,000,000	70,000,000
Capital costs																						44,200,000	44,200,000
Maintenance expenses																						25,800,000	25,800,000
Overall annual rate increase of the projected deferred under-recovered balance related to non-utility generators																52,200,000		55,300,000	55,300,000
Contributions received by ACE																				11,000,000	11,000,000
Basis point																				0.50%																							0.50%																								0.50%
New power plant output					661							650			700																														661									650			700													661													650			700
Undergrounding project cost		1,000,000,000																																																													1,000,000,000
Bear estimated complete project																																																															500,000,000																										500,000,000
Underground project cost								375,000,000																																																							375,000,000
Number of District of Columbia's outage-prone power lines to bury									60																																																																60
Congressional review period									30 days																																																																30 days
Recovery			88,000,000																																									38,000,000																								50,000,000
Recovery period			5 years				3 years																									3 years												5 years																								5 years				3 years
Length transmission line			152																																									152																								152
Abandoned costs				68,000,000																																							31,000,000																								37,000,000
Net of amortization				14,000,000																																							6,000,000																								8,000,000
Abandoned cost original value				88,000,000																																							38,000,000																								50,000,000
Disallowed costs written off				2,000,000																																							1,000,000																								1,000,000
Abandoned costs transferred to inventories				4,000,000																																																															4,000,000
Regulatory asset, amortization period, years																												1 year		20 years																							1 year			20 years																										1 year			20 years
Goodwill transferred to a regulatory asset																																											$ 41,000,000
Return earned, deferral																																											12.95%
Transition bond maturity, lower range																				2013
Transition bond maturity, upper range																				2023