Regulatory Matters - Additional Information (Detail) (USD $)	0 Months Ended		1 Months Ended						3 Months Ended	12 Months Ended			1 Months Ended						0 Months Ended					1 Months Ended			3 Months Ended		3 Months Ended	0 Months Ended	3 Months Ended	0 Months Ended			1 Months Ended		0 Months Ended			1 Months Ended	3 Months Ended			0 Months Ended		0 Months Ended	1 Months Ended	0 Months Ended								1 Months Ended		3 Months Ended				0 Months Ended	3 Months Ended				3 Months Ended	12 Months Ended		0 Months Ended		0 Months Ended			1 Months Ended		3 Months Ended	0 Months Ended	3 Months Ended	0 Months Ended			1 Months Ended
	Apr. 02, 2014	Mar. 26, 2014	Mar. 31, 2014 mi	Aug. 31, 2013	May 31, 2013	Dec. 31, 2012	Jul. 31, 2012	Dec. 31, 2011	Mar. 31, 2014	Dec. 31, 2013	Feb. 28, 2014	Apr. 30, 2012 MW	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, 2011 Expected [Member]	Dec. 31, 2011 Actual [Member]	Apr. 30, 2012 Minimum [Member] MW	Apr. 30, 2012 Maximum [Member] MW	Mar. 26, 2014 Potomac Electric Power Co [Member]	Dec. 03, 2013 Potomac Electric Power Co [Member]	Jul. 12, 2013 Potomac Electric Power Co [Member]	Mar. 08, 2013 Potomac Electric Power Co [Member]	Aug. 24, 2012 Potomac Electric Power Co [Member] mi	Nov. 30, 2012 Potomac Electric Power Co [Member]	Jul. 31, 2012 Potomac Electric Power Co [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member]	Mar. 31, 2014 Potomac Electric Power Co [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] MW	Mar. 31, 2014 Potomac Electric Power Co [Member] District of Columbia [Member]	Feb. 27, 2013 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Mar. 31, 2014 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Mar. 26, 2014 Potomac Electric Power Co [Member] Expected [Member]	Dec. 04, 2013 Potomac Electric Power Co [Member] Expected [Member]	Dec. 03, 2013 Potomac Electric Power Co [Member] Expected [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member] Expected [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member] Actual [Member]	Apr. 15, 2014 Potomac Electric Power Co [Member] Scenario Forecast [Member]	Mar. 08, 2013 Potomac Electric Power Co [Member] Adjusted [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member]	Mar. 31, 2014 Potomac Electric Power Co [Member]	Feb. 28, 2014 Potomac Electric Power Co [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]	Apr. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] MW	Feb. 27, 2013 Potomac Electric Power Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] Expected [Member]	Dec. 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]	Sep. 20, 2013 Delmarva Power & Light Co/De [Member]	Aug. 28, 2013 Delmarva Power & Light Co/De [Member]	Jun. 01, 2013 Delmarva Power & Light Co/De [Member]	Mar. 22, 2013 Delmarva Power & Light Co/De [Member]	Apr. 02, 2012 Delmarva Power & Light Co/De [Member]	Mar. 31, 2013 Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member]	Mar. 31, 2014 Delmarva Power & Light Co/De [Member] mi	Feb. 28, 2014 Delmarva Power & Light Co/De [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] MW	Mar. 31, 2014 Delmarva Power & Light Co/De [Member] Advanced Metering Infrastructure Costs [Member]	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Mar. 31, 2014 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Apr. 01, 2015 Delmarva Power & Light Co/De [Member] Scenario Forecast [Member] Advanced Metering Infrastructure Costs [Member]	Jul. 01, 2014 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. 31, 2014 Delmarva Power & Light Co/De [Member]	Dec. 31, 2015 Delmarva Power & Light Co/De [Member] Scenario Forecast [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]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] MW	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Mar. 14, 2014 Atlantic City Electric Co [Member]	Mar. 03, 2014 Atlantic City Electric Co [Member]	May 31, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member]	Mar. 31, 2014 Atlantic City Electric Co [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Mar. 31, 2014 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Apr. 16, 2014 Atlantic City Electric Co [Member] Scenario Forecast [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	May 31, 2013 PHI [Member]
Regulatory Matters [Line Items]
Requested rate change		$ 23,400,000	$ 61,700,000				$ 18,100,000								$ 68,400,000	$ 66,200,000				$ 44,800,000		$ 52,100,000		$ 60,800,000	$ 18,100,000	$ 68,400,000						$ 23,400,000	$ 43,300,000	$ 43,300,000	$ 60,800,000	$ 66,200,000		$ 44,800,000												$ 56,000,000	$ 39,000,000			$ 42,000,000	$ 15,100,000	$ 39,000,000																	$ 61,700,000
Return on equity, percentage		9.40%	10.25%				9.31%	10.75%											9.40%	10.25%	9.36%	10.25%		10.25%	9.31%	10.75%	10.80%			8.70%	11.30%		10.25%	10.25%										6.78%		10.33%			9.70%					10.25%	9.70%	10.25%		10.80%				8.70%	11.30%							6.78%		10.33%	10.25%				10.80%	8.70%	11.30%		6.78%	10.33%
Interim rate increase implemented																																																					2,500,000
Additional interim rate increase implemented	15,100,000																																																25,100,000
Interim rates in effect subject to refund																																																	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
Base rate period																																																													2 years			2 years		2 years
Portion of advanced metering infrastructure in percentage																																																																50.00%	50.00%	50.00%
Effect of proposed change on gas cost rate				(5.50%)																																																(5.50%)
Surcharge for recovery of costs																																			192,000,000
Proposed incentive for meeting enhanced reliability goals																																			1,000,000												1,000,000
Credit to customers																																															1,000,000
Requested rate change																					27,900,000								23,400,000
Deferred operation and maintenance expenses																					23,600,000
Period of amortized expenses																					5 years
Charges on cost of recovery																					24,000,000
Adjusted rate change																																					37,400,000
Overall annual rate increase as net impact of adjusting charges																																																																											52,200,000	55,300,000				41,100,000
Overall annual rate increase as net impact of adjusting charges																																																																										24,500,000
Contributions received by ACE																																																																													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
Bear estimated complete project																																																																																			500,000,000
Underground project cost													375,000,000
Number of District of Columbia's outage-prone power lines to bury														60
Congressional review period														30 days
Abandonment costs sought			80,500,000			88,000,000				82,000,000																													45,000,000	50,000,000	43,900,000							37,000,000									38,000,000	36,600,000
Recovery period			3 years																																						3 years																3 years
Estimated fair value of real property acquired											8,000,000																															2,000,000																	6,000,000
Length transmission line			152																				152																																			152
Abandoned costs			52,000,000						52,000,000
Net of amortization			8,000,000						8,000,000
Abandoned cost original value									3,000,000																																																	3,000,000
Abandoned cost original value of second year									1,000,000																																																											2,000,000
Return on equity, percentage																					9.36%								9.40%
Land held for future use in utility operations																																									2,000,000																										6,000,000
Regulatory asset related to MAPP abandonment costs																																									30,000,000																										22,000,000
Disallowed costs written off																																																										$ 1,000,000