Regulatory Matters - Additional Information (Detail)											1 Months Ended														12 Months Ended		30 Months Ended
	Feb. 01, 2016 USD ($)	Nov. 06, 2015 USD ($)	Sep. 11, 2015 USD ($)	Jun. 01, 2015 USD ($)	May. 19, 2015 USD ($)	Apr. 17, 2015 USD ($)	Dec. 08, 2014	Dec. 07, 2014	Apr. 15, 2014 USD ($)	Sep. 20, 2013 USD ($)	Aug. 31, 2015	Mar. 31, 2015 USD ($)	Oct. 31, 2014	Aug. 31, 2014 USD ($)	Jul. 31, 2014 USD ($)	May. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Oct. 31, 2013 USD ($)	Jul. 31, 2013 USD ($)	Mar. 31, 2013 USD ($)	Feb. 28, 2013	Nov. 30, 2012 USD ($)	Jul. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2011	Dec. 31, 2015 USD ($)	Apr. 30, 2012 MW
Public Utilities, General Disclosures [Line Items]
Transition bond maturity, lower range																									2016
Transition bond maturity, upper range																									2023
Date of acquisition																									Apr. 29, 2014
Return on equity, percentage		10.00%																	9.36%					10.75%
Approved rate change															$ 8,750,000				$ 27,900,000				$ 18,100,000
Return on equity, percentage															9.62%								9.31%
Effect of proposed change on Gas Cost Rate											26.00%
Adjusted rate change									$ 37,400,000
Charges on cost of recovery																			$ 24,000,000
Consolidated tax adjustment calculation review period													5 years
Percentage of revenue requirement related to consolidated tax adjustment calculation													25.00%
Basis-point		0.50%
Return of equity effective date		Mar. 08, 2016
New power plant output | MW																												661
Undergrounding project cost																$ 1,000,000,000
Entity share to complete project																500,000,000
Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							8.80%	10.80%
Reserve for litigation filed																									$ 32,000,000		$ 32,000,000
Expected [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change																	$ 43,300,000					$ 60,800,000		$ 68,400,000
Return on equity, percentage																	10.25%
Actual [Member]
Public Utilities, General Disclosures [Line Items]
Adjusted rate change																								66,200,000
District of Columbia [Member] | DC Undergrounding Task Force [Member]
Public Utilities, General Disclosures [Line Items]
Underground project cost																375,000,000
MAPP Abandonment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Project termination costs																									Aug. 24, 2012
Amortization and recovery period																									2016-05
Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									1 year
New power plant output | MW																												650
Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									20 years
New power plant output | MW																												700
Maximum [Member] | District of Columbia [Member] | Department of Transportation [Member]
Public Utilities, General Disclosures [Line Items]
Under grounding project costs covered by existing capital projects program																125,000,000
Pepco and Delmarva Power Light Co [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Storm Restoration Costs Amortization and recovery period																										5 years
Delmarva Power & Light Co/De [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change										$ 39,000,000								$ 56,000,000		$ 42,000,000
Return on equity, percentage		10.00%												9.70%						10.25%					10.80%
Approved rate change														$ 15,100,000
Return on equity, percentage														9.70%
Increased distribution base period																		4 years
Estimated return on equity, year one																		7.41%
Estimated return on equity, year two																		8.80%
Estimated return on equity, year three																		9.75%
Estimated return on equity, year four																		9.75%
Customer refundable fees																		$ 500,000
Effect of proposed change on Gas Cost Rate											26.00%
Basis-point		0.50%																							0.50%		0.50%
Return of equity effective date		Mar. 08, 2016
Customer refunds		$ 11,900,000
New power plant output | MW																												661
Goodwill transferred to a regulatory asset																									$ 41,000,000		$ 41,000,000
Return earned on regulatory assets																									12.95%		12.95%
Delmarva Power & Light Co/De [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							8.80%	10.80%													8.70%				11.30%
Reserve for litigation filed																									$ 11,000,000		$ 11,000,000
Delmarva Power & Light Co/De [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									1 year
New power plant output | MW																												650
Delmarva Power & Light Co/De [Member] | Minimum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																					6.78%
Delmarva Power & Light Co/De [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									20 years
New power plant output | MW																												700
Delmarva Power & Light Co/De [Member] | Maximum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																					10.33%
Atlantic City Electric Co [Member]
Public Utilities, General Disclosures [Line Items]
Transition bond maturity, lower range																									2016
Transition bond maturity, upper range																									2023
Incremental Storm Restoration Costs Amortization and recovery period																										3 years
Requested rate change						$ 33,900,000						$ 52,000,000
Return on equity, percentage		10.00%																							10.80%
Approved rate change			$ 32,600,000	$ (1,300,000)	$ 33,900,000
Contributions received by ACE																									$ 11,000,000		$ 11,000,000
Consolidated tax adjustment calculation review period													5 years
Percentage of revenue requirement related to consolidated tax adjustment calculation													25.00%
Basis-point																									0.50%		0.50%
Return of equity effective date		Mar. 08, 2016
Customer refunds		$ 9,500,000
Atlantic City Electric Co [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Overall annual rate increase as net impact of adjusting charges	$ 8,800,000
Atlantic City Electric Co [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							8.80%	10.80%													8.70%				11.30%
Reserve for litigation filed																									$ 8,000,000		$ 8,000,000
Atlantic City Electric Co [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									1 year
Atlantic City Electric Co [Member] | Minimum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																					6.78%
Atlantic City Electric Co [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									20 years
Contributions paid by ACE																											$ 1,000,000
Atlantic City Electric Co [Member] | Maximum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																					10.33%
Potomac Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change																								$ 68,400,000
Return on equity, percentage		10.00%																	9.36%			10.25%		10.75%	10.80%
Approved rate change															$ 8,750,000				$ 27,900,000				$ 18,100,000
Return on equity, percentage															9.62%				9.36%				9.31%
Adjusted rate change									$ 37,400,000
Charges on cost of recovery																			$ 24,000,000
Basis-point		0.50%																							0.50%		0.50%
Return of equity effective date		Mar. 08, 2016
Customer refunds		$ 14,200,000
New power plant output | MW																												661
Undergrounding project cost																1,000,000,000
Entity share to complete project																500,000,000
Potomac Electric Power Co [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							8.80%	10.80%													8.70%				11.30%
Reserve for litigation filed																									$ 13,000,000		$ 13,000,000
Potomac Electric Power Co [Member] | Expected [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change																	$ 43,300,000					$ 60,800,000
Return on equity, percentage																	10.25%
Potomac Electric Power Co [Member] | Actual [Member]
Public Utilities, General Disclosures [Line Items]
Adjusted rate change																								$ 66,200,000
Potomac Electric Power Co [Member] | District of Columbia [Member] | DC Undergrounding Task Force [Member]
Public Utilities, General Disclosures [Line Items]
Underground project cost																375,000,000
Potomac Electric Power Co [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									1 year
New power plant output | MW																												650
Potomac Electric Power Co [Member] | Minimum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																					6.78%
Potomac Electric Power Co [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years																									20 years
New power plant output | MW																												700
Potomac Electric Power Co [Member] | Maximum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																					10.33%
Potomac Electric Power Co [Member] | Maximum [Member] | District of Columbia [Member] | Department of Transportation [Member]
Public Utilities, General Disclosures [Line Items]
Under grounding project costs covered by existing capital projects program																$ 125,000,000