Debt (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended			12 Months Ended							12 Months Ended	3 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	12 Months Ended	0 Months Ended		3 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2011 days	Dec. 31, 2010	Jan. 31, 2012	Dec. 31, 2011 Delmarva Power & Light Co/De [Member] days	Dec. 31, 2011 Pepco Energy Services [Member]	Dec. 31, 2010 Pepco Energy Services [Member]	Dec. 31, 2009 Pepco Energy Services [Member]	Dec. 31, 2011 Atlantic City Electric Co [Member] days	Dec. 31, 2011 Potomac Electric Power Co [Member] days	Jun. 30, 2011 Tax-Exempt Bonds [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 First Mortgage Bonds [Member]	Jun. 30, 2011 First Mortgage Bonds [Member] Atlantic City Electric Co [Member]	Nov. 30, 2010 5.90% Due 2016 [Member]	Dec. 31, 2011 5.90% Due 2016 [Member] Unsecured Notes [Member]	Nov. 30, 2010 6.00% Due 2019 [Member]	Jul. 20, 2010 6.125% Due 2017 [Member]	Oct. 31, 2010 6.125% Due 2017 [Member]	Dec. 31, 2011 6.125% Due 2017 [Member] Unsecured Notes [Member]	Jul. 02, 2010 6.45% Due 2012 [Member]	Jul. 08, 2010 6.45% Due 2012 [Member]	Sep. 30, 2010 6.45% Due 2012 [Member]	Jul. 20, 2010 7.45% Due 2032 [Member]	Dec. 31, 2011 7.45% Due 2032 [Member] Unsecured Notes [Member]
Debt Instrument [Line Items]
Maturities of long term debt, 2012			$ 110,000,000
Maturities of long term debt, 2013			558,000,000
Maturities of long term debt, 2014			334,000,000
Maturities of long term debt, 2015			409,000,000
Maturities of long term debt, 2016			338,000,000
Maturities of long term debt, thereafter			2,462,000,000				7,000,000
Total long term project funding	2,000,000			2,000,000			15,000,000	19,000,000
Long term debt maturing 2012 through 2014							2,000,000
Long term debt maturing 2015 through 2016							1,000,000
Ongoing commercial paper			875,000,000		1,250,000,000	500,000,000				250,000,000	500,000,000
Commercial paper outstanding			465,000,000			47,000,000					74,000,000
Commercial paper weighted average interest rate			0.64%			0.34%				0.33%	0.35%
Commercial paper weighted average maturity, in days			11			2				6	2
Variable rate demand bonds amount						105,000,000	18,000,000			23,000,000			72,000,000
Variable rate demand bonds maturing 2014 to 2017			49,000,000
Variable rate demand bonds maturing 2024			33,000,000
Variable rate demand bonds weighted average interest rate			0.44%	0.45%
Variable rate demand bonds maturing 2028 to 2031			64,000,000
Line of credit facility, maximum borrowing capacity			1,500,000,000
Line of credit facility, expiration date			August 1, 2016
Ratio of total indebtedness to total capitalization, percentage			65
Ratio of deferrable interest subordinated debt to net capital, percentage			15
Debt instrument variable interest rate, interest rate before LIBOR			0.50%
Parent company borrowing limit under credit facility			500,000,000
Maximum amount of credit available to parent			1,250,000,000
Subsidiary borrowing limit under parent's credit facility			500,000,000
Carrying value of instrument	3,675,000,000		3,879,000,000	3,675,000,000								35,000,000		200,000,000
Borrowing capacity under the credit facilities	1,200,000,000		1,000,000,000	1,200,000,000
Combined cash and borrowings capacity	462,000,000		711,000,000	462,000,000
Loss on extinguishment of debt	(54,000,000)	(135,000,000)		(189,000,000)																			(120,000,000)
Loss on extinguishment of debt, net				113,000,000
Debt interest percentage														4.35%		5.90%				6.125%					7.45%
Debt instrument maturity date														April 1, 2021		2016				2017					2032
Redemption of outstanding debt															10,000,000		200,000,000	129,000,000	40,000,000		640,000,000	110,000,000		65,000,000
Accelerated recognition of hedging losses				15,000,000
Line of credit facility, collateral fees									25,000,000
Interest expense, debt							1,000,000	8,000,000	16,000,000
Cash collateral posted							112,000,000	117,000,000
Credit facility borrowing capacity			750,000,000			250,000,000	283,000,000	728,000,000		250,000,000	250,000,000
Letters of credit posted							$ 1,000,000	$ 113,000,000