Commitments And Contingencies (Schedule Of Accrued Liabilities For Environmental Exposures) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Commitments And Contingencies [Line Items]
Beginning balance	$ 30
Accruals
Payments	(1)
Ending balance	29
Less amounts in Other current liabilities	6
Amounts in Other deferred credits	23
Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	18
Accruals
Payments	(1)
Ending balance	17
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	16
Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	7
Accruals
Payments	(1)
Ending balance	6
Less amounts in Other current liabilities	4
Amounts in Other deferred credits	2
Transmission And Distribution [Member]
Commitments And Contingencies [Line Items]
Beginning balance	15
Accruals
Ending balance	15
Less amounts in Other current liabilities	2
Amounts in Other deferred credits	13
Transmission And Distribution [Member] | Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	14
Accruals
Ending balance	14
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	13
Transmission And Distribution [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	1
Accruals
Ending balance	1
Less amounts in Other current liabilities	1
Regulated [Member]
Commitments And Contingencies [Line Items]
Beginning balance	8
Accruals
Payments	(1)
Ending balance	7
Less amounts in Other current liabilities	2
Amounts in Other deferred credits	5
Regulated [Member] | Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	4
Accruals
Payments	(1)
Ending balance	3
Amounts in Other deferred credits	3
Regulated [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	4
Accruals
Payments	(1)
Ending balance	3
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	2
Regulated [Member] | Atlantic City Electric Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	1
Accruals
Ending balance	1
Amounts in Other deferred credits	1
Non-Regulated [Member]
Commitments And Contingencies [Line Items]
Beginning balance	5
Accruals
Ending balance	5
Amounts in Other deferred credits	5
Other [Member]
Commitments And Contingencies [Line Items]
Beginning balance	2
Accruals
Ending balance	2
Less amounts in Other current liabilities	2
Other [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	2
Accruals
Ending balance	2
Less amounts in Other current liabilities	$ 2