Debt - Additional Information (Detail) (USD $)	0 Months Ended	9 Months Ended		1 Months Ended			9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended		9 Months Ended			9 Months Ended			0 Months Ended		1 Months Ended					9 Months Ended	1 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended		0 Months Ended		9 Months Ended
	Mar. 13, 2014	Sep. 30, 2014 Sublimit	Dec. 31, 2013	Oct. 31, 2014 Subsequent Event [Member] Bonds and Debentures [Member]	Oct. 31, 2014 Subsequent Event [Member] Bonds and Notes [Member]	Aug. 31, 2014 First Mortgage Bonds [Member] 7.63% Secured Medium Term Notes, Due 2014 [Member]	Sep. 30, 2014 First Mortgage Bonds [Member] 7.63% Secured Medium Term Notes, Due 2014 [Member]	Aug. 21, 2014 First Mortgage Bonds [Member] May.10, 2013 ACE Term Loan Repaid Aug. 21, 2014 [Member]	Sep. 30, 2014 Maximum [Member]	Mar. 13, 2014 Potomac Electric Power Co [Member]	Sep. 30, 2014 Potomac Electric Power Co [Member] Sublimit	Dec. 31, 2013 Potomac Electric Power Co [Member]	Sep. 30, 2014 Potomac Electric Power Co [Member] Maximum [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Sublimit	Dec. 31, 2013 Delmarva Power & Light Co/De [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Maximum [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member] Sublimit	Dec. 31, 2013 Atlantic City Electric Co [Member]	May 10, 2013 Atlantic City Electric Co [Member] Term Loan Agreement [Member]	May 10, 2013 Atlantic City Electric Co [Member] Term Loan Agreement [Member]	Jul. 31, 2014 Atlantic City Electric Co [Member] Bonds and Debentures [Member]	Jul. 31, 2014 Atlantic City Electric Co [Member] Bonds and Notes [Member]	Oct. 31, 2014 Atlantic City Electric Co [Member] Subsequent Event [Member] Bonds and Debentures [Member]	Oct. 31, 2014 Atlantic City Electric Co [Member] Subsequent Event [Member] Bonds and Notes [Member]	Aug. 31, 2014 Atlantic City Electric Co [Member] First Mortgage Bonds [Member] 3.375% Due 2024 [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member] First Mortgage Bonds [Member] 3.375% Due 2024 [Member]	Aug. 31, 2014 Atlantic City Electric Co [Member] First Mortgage Bonds [Member] 7.63% Secured Medium Term Notes, Due 2014 [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member] First Mortgage Bonds [Member] 7.63% Secured Medium Term Notes, Due 2014 [Member]	Aug. 21, 2014 Atlantic City Electric Co [Member] First Mortgage Bonds [Member] May.10, 2013 ACE Term Loan Repaid Aug. 21, 2014 [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member] Maximum [Member]	Sep. 30, 2014 PHI [Member]	May 29, 2013 PHI [Member] Term Loan Agreement [Member]	Mar. 28, 2013 PHI [Member] Term Loan Agreement [Member]	Sep. 30, 2014 PHI [Member] Term Loan Agreement [Member]	Mar. 28, 2013 PHI [Member] Term Loan Agreement [Member]
Debt Instrument [Line Items]
Credit facility, termination date		Aug. 01, 2018									Aug. 01, 2018			Aug. 01, 2018			Aug. 01, 2018
Line of credit facility maximum borrowing capacity		$ 1,500,000,000									$ 1,500,000,000
Parent company credit facility letters of credit, maximum		500,000,000									500,000,000
Same day borrowings maximum percentage amount		10.00%									10.00%						10.00%
Swingline loan repayment period		14 days									14 days						14 days
Credit facility borrowing capacity		750,000,000									250,000,000			250,000,000			250,000,000
Maximum amount of credit available to parent		1,250,000,000
Subsidiary borrowing limit under parent's credit facility									500,000,000		500,000,000			500,000,000			500,000,000
Maximum number of sublimit reallocations per year		8									8			8			8
Debt instrument variable interest rate in addition to the federal funds effective rate		0.50%									0.50%			0.50%			0.50%
Debt instrument variable interest rate in addition to one month LIBOR's effective rate		1.00%									1.00%			1.00%			1.00%
Ratio of indebtedness to total capitalization													65.00%			65.00%														65.00%
Ratio of deferrable interest subordinated debt to total capitalization													15.00%			15.00%														15.00%
Borrowing capacity under the credit facility		1,305,000,000	1,063,000,000
Utility subsidiaries combined cash and borrowing capacity		885,000,000	332,000,000								885,000,000	332,000,000		885,000,000	332,000,000		885,000,000	332,000,000
Amended description of Change in Control		The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.									The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.			The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.			The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.
Ownership percentage of outstanding voting stock for Change in Control		100.00%									100.00%			100.00%			100.00%
On-going commercial paper		875,000,000									500,000,000			500,000,000			350,000,000
Commercial paper outstanding		329,000,000									0			0			99,000,000
Commercial paper weighted average interest rate		0.51%									0.27%			0.26%			0.25%
Commercial paper weighted average maturity, in days		5 days									6 days			5 days			4 days
Debt instrument, carrying value																															200,000,000				250,000,000
Debt instrument, maturity date							Aug. 29, 2014																			Sep. 01, 2024		Aug. 29, 2014						Mar. 27, 2014
Margin added to stated rate																			0.75%														0.875%
PHI repaid loan																																250,000,000
Debt instrument, face amount																				100,000,000					150,000,000
Debt instrument, interest percentage						7.63%																			3.375%		7.63%
Net proceeds from issuance of bonds																									7,200,000
Repayment of first mortgage bonds						7,000,000																					7,000,000
Prepayment of term loan								100,000,000																					100,000,000
Debt instrument periodical principal payments				9,000,000	3,000,000																7,000,000	3,000,000	9,000,000	3,000,000
Purchase price	$ 12,000,000	$ 10,000,000								$ 12,000,000	$ 10,000,000
Contract payment period		9 years									9 years