Debt - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended						12 Months Ended				12 Months Ended			0 Months Ended		12 Months Ended			12 Months Ended					12 Months Ended		0 Months Ended	12 Months Ended						12 Months Ended		12 Months Ended			12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended		12 Months Ended	0 Months Ended						12 Months Ended			12 Months Ended				0 Months Ended		12 Months Ended
	Aug. 02, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Medium-Term Notes [Member]	Dec. 31, 2012 Medium-Term Notes [Member]	Dec. 31, 2013 First Mortgage Bonds [Member]	Dec. 31, 2012 First Mortgage Bonds [Member]	Dec. 31, 2013 First Mortgage Bonds [Member] 4.15% Due 2043 [Member]	Dec. 31, 2013 First Mortgage Bonds [Member] 4.95% Due 2043 [Member]	Dec. 31, 2013 First Mortgage Bonds [Member] 4.95% Due 2013 [Member]	Dec. 31, 2012 First Mortgage Bonds [Member] 4.95% Due 2013 [Member]	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2013 Maximum [Member] Term Loan Agreement [Member]	Dec. 31, 2013 Restated Agreement [Member]	Oct. 24, 2013 Construction Financing [Member]	Aug. 02, 2011 Potomac Electric Power Co [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] Medium-Term Notes [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] First Mortgage Bonds [Member] 4.15% Due 2043 [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] First Mortgage Bonds [Member] 4.95% Due 2043 [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] First Mortgage Bonds [Member] 4.95% Due 2013 [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member] First Mortgage Bonds [Member] 4.95% Due 2013 [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] Senior Notes [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] Maximum [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member] Restated Agreement [Member]	Aug. 02, 2011 Delmarva Power & Light Co/De [Member]	Dec. 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] Medium-Term Notes [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member] Medium-Term Notes [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Unsecured Tax-Exempt Bonds [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member] Unsecured Tax-Exempt Bonds [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] First Mortgage Bonds [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member] First Mortgage Bonds [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] First Mortgage Bonds [Member] 3.50% Due 2023 [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] First Mortgage Bonds [Member] 6.40% Due 2013 [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member] First Mortgage Bonds [Member] 6.40% Due 2013 [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member] Restated Agreement [Member]	Aug. 02, 2011 Atlantic City Electric Co [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member]	May 10, 2013 Atlantic City Electric Co [Member] Term Loan Agreement [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Term Loan Agreement [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Six Point Six Two Five Percentage Due Two Thousand Thirteen [Member]	May 10, 2013 Atlantic City Electric Co [Member] In Addition to Federal Funds Rate [Member]	May 10, 2013 Atlantic City Electric Co [Member] Eurodollar [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Senior Medium Term Notes One [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Unsecured Tax-Exempt Bonds [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] First Mortgage Bonds [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member] First Mortgage Bonds [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] First Mortgage Bonds [Member] Six Point Six Two Five Percentage Due Two Thousand Thirteen [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Transition Bonds [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member] Transition Bonds [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Maximum [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Maximum [Member] Term Loan Agreement [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Restated Agreement [Member]	Dec. 31, 2013 PHI [Member]	May 29, 2013 PHI [Member] Term Loan Agreement [Member]	Mar. 28, 2013 PHI [Member] Term Loan Agreement [Member]	Dec. 31, 2013 PHI [Member] Term Loan Agreement [Member]	Dec. 31, 2013 Pepco Energy Services [Member]	Dec. 31, 2012 Pepco Energy Services [Member]
Debt Instrument [Line Items]
Principal amount of debt								$ 250,000,000	$ 150,000,000										$ 110,000,000	$ 250,000,000	$ 150,000,000			$ 1,060,000,000						$ 100,000,000						$ 300,000,000													$ 249,000,000	$ 62,000,000
Debt instrument, maturity date								Mar. 15, 2043	Nov. 15, 2043											Mar. 15, 2043	Nov. 15, 2043															Nov. 15, 2023								Nov. 10, 2014																		Mar. 27, 2014
Debt instrument, interest percentage								4.15%	4.95%	4.95%										4.15%	4.95%	4.95%														3.50%	6.40%								0.92%	6.63%							6.63%
Repayment of first mortgage bonds										200,000,000												200,000,000						100,000,000									250,000,000									69,000,000							69,000,000
Amount Received in construction financing		1,500,000,000													8,000,000
Interest rate of amount received in construction financing															4.68%
Duration to repay the financing															23 years
Pollution control revenue																																														4,000,000							4,000,000
Maturities of long term debt, 2014		444,000,000															175,000,000											100,000,000														107,000,000												41,000,000									2,000,000
Maturities of long term debt, 2015		409,000,000															0											100,000,000														15,000,000												44,000,000									2,000,000
Maturities of long term debt, 2016		338,000,000															0											100,000,000														2,000,000												46,000,000									1,000,000
Maturities of long term debt, 2017		133,000,000															0											14,000,000														0												35,000,000									1,000,000
Maturities of long term debt, 2018		286,000,000															0											4,000,000														250,000,000												31,000,000									2,000,000
Total long term project funding																																																															12,000,000	13,000,000
Maturities of long term debt, thereafter																	1,735,000,000											650,000,000														487,000,000												58,000,000									4,000,000
Ongoing commercial paper		875,000,000															500,000,000											500,000,000														350,000,000
Commercial paper outstanding		24,000,000	264,000,000														151,000,000	231,000,000										147,000,000	32,000,000													120,000,000	110,000,000
Commercial paper weighted average interest rate		0.70%	0.87%														0.34%	0.43%										0.29%	0.43%													0.31%	0.41%
Commercial paper weighted average maturity, in days		5 days	10 days														5 days	5 days										3 days	4 days													4 days	3 days
Variable rate demand bonds amount																												105,000,000						72,000,000								18,000,000
Variable rate demand bonds maturing 2014 to 2017		44,000,000
Variable rate demand bonds maturing 2024		33,000,000																										33,000,000
Variable rate demand bonds maturing 2028 to 2029		46,000,000
Variable rate demand bonds weighted average interest rate		0.24%	0.34%																									0.26%	0.38%													0.11%	0.18%
Line of credit facility, expiration date	Aug. 02, 2012															Aug. 02, 2012											Aug. 02, 2012														Aug. 02, 2012
Line of credit facility, extended expiration date		August 1, 2017												August 1, 2018			August 1, 2017									August 1, 2018		August 1, 2017												August 1, 2018		August 1, 2017																August 1, 2018
Parent company credit facility letter of credit, maximum		500,000,000
Same day borrowings maximum percentage amount		10.00%															10.00%											10.00%														10.00%
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
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%														65.00%																	65.00%	65.00%
Ratio of deferrable interest subordinated debt to total capitalization												15.00%	15.00%												15.00%														15.00%																	15.00%	15.00%
Borrowing capacity under the credit facility		1,063,000,000	861,000,000														332,000,000	477,000,000										332,000,000	477,000,000													332,000,000	477,000,000
Utility subsidiaries combined cash and borrowing capacity		332,000,000	477,000,000																									332,000,000	477,000,000
Debt instrument, carrying value		4,470,000,000	4,190,000,000														1,910,000,000	1,710,000,000										968,000,000	918,000,000													861,000,000	830,000,000								761,000,000	830,000,000		255,000,000	295,000,000				200,000,000		250,000,000
Margin added to stated rate																																												0.75%			0.50%	1.00%													0.875%
PHI repaid loan																																																												250,000,000
Debt instrument, carrying value																																												100,000,000
Variable rate demand bonds maturing 2017																												26,000,000
Variable rate demand bonds maturing 2028																												16,000,000
Variable rate demand bonds maturing 2029																												30,000,000
Debt instrument, carrying value		$ 906,000,000	$ 906,000,000	$ 40,000,000	$ 40,000,000	$ 3,321,000,000	$ 3,140,000,000	$ 250,000,000	$ 150,000,000		$ 200,000,000									$ 250,000,000	$ 150,000,000		$ 200,000,000							$ 40,000,000	$ 40,000,000	$ 78,000,000	$ 78,000,000	$ 650,000,000	$ 600,000,000	$ 300,000,000		$ 250,000,000						$ 100,000,000