Pension And Other Postretirement Benefits (Narrative) (Details) (USD $)	12 Months Ended																		0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended						12 Months Ended
	Dec. 31, 2011 employees	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2011 Potomac Electric Power Co [Member]	Dec. 31, 2010 Potomac Electric Power Co [Member]	Dec. 31, 2009 Potomac Electric Power Co [Member]	Dec. 31, 2011 Atlantic City Electric Co [Member]	Dec. 31, 2009 Atlantic City Electric Co [Member]	Dec. 31, 2011 Delmarva Power & Light Co/De [Member]	Dec. 31, 2009 Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Pension Benefits [Member]	Dec. 31, 2010 Pension Benefits [Member]	Dec. 31, 2009 Pension Benefits [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member]	Dec. 31, 2010 Other Postretirement Benefits [Member]	Dec. 31, 2009 Other Postretirement Benefits [Member]	Jan. 31, 2012 Other Postretirement Benefits [Member] Potomac Electric Power Co [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Potomac Electric Power Co [Member]	Dec. 31, 2010 Other Postretirement Benefits [Member] Potomac Electric Power Co [Member]	Jan. 31, 2012 Other Postretirement Benefits [Member] Atlantic City Electric Co [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Atlantic City Electric Co [Member]	Dec. 31, 2010 Other Postretirement Benefits [Member] Atlantic City Electric Co [Member]	Jan. 31, 2012 Other Postretirement Benefits [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2010 Other Postretirement Benefits [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Subsidiaries [Member]	Dec. 31, 2010 Other Postretirement Benefits [Member] Subsidiaries [Member]	Dec. 31, 2010 Retirement Plan [Member]	Dec. 31, 2011 Retirement Plan [Member]	Dec. 31, 2011 Retirement Plan [Member] Potomac Electric Power Co [Member]	Dec. 31, 2011 Retirement Plan [Member] Atlantic City Electric Co [Member]	Dec. 31, 2011 Retirement Plan [Member] Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Medicare Part D subsidy receipts	$ 2,000,000	$ 3,000,000				$ 2,000,000	$ 3,000,000
Retirement Plan assets	1,700,000,000	1,600,000,000
Accumulated benefit obligation	2,000,000,000	1,900,000,000											2,124,000,000	1,970,000,000	1,796,000,000	750,000,000	704,000,000	651,000,000
Net loss to be amortized from AOCL into net periodic benefit cost													55,000,000			18,000,000
Prior service cost to be amortized from AOCL into net periodic benefit cost													1,000,000			5,000,000
Expected long-term return on plan assets	7.75%												7.75%	8.00%	8.25%	7.75%	8.00%	8.25%
Medical trend rate assumed for next fiscal year				8.00%	7.00%											8.00%	7.50%
Number of employees affected by changes to retirement plan	750
Number of pre-existing supplemental retirement plans	2
Direction and pattern of medical trend rate				declining 0.5% per year to a rate of 5.0% for 2017 to 2018 and beyond	declining 0.5% per year to a rate of 5.0% for 2015 to 2016 and beyond
Unfunded capital commitments	28,000,000	42,000,000
Pension contributions	110,000,000	100,000,000	300,000,000			40,000,000		170,000,000	30,000,000	60,000,000	40,000,000	10,000,000							85,000,000	7,000,000	10,000,000	30,000,000	7,000,000	8,000,000	85,000,000	6,000,000	9,000,000	13,000,000	8,000,000	100,000,000		40,000,000	30,000,000	40,000,000
Percentage of participants vested	100.00%
Defined contribution plan matching contributions	$ 11,000,000	$ 11,000,000	$ 12,000,000
Asset allocation, percentage in equity investments																62.00%	61.00%													53.00%	36.00%
Asset allocation, percentage in other investments																														7.00%	8.00%