Commitments And Contingencies (Schedule Of Accrued Liabilities For Environmental Exposures) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Commitments And Contingencies [Line Items]
Beginning balance	$ 29
Accruals
Payments	1
Ending balance	28
Less amounts in Other current liabilities	5
Amounts in Other deferred credits	23
Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	17
Accruals
Payments
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	6
Accruals
Payments	1
Ending balance	5
Less amounts in Other current liabilities	4
Amounts in Other deferred credits	1
Transmission And Distribution [Member]
Commitments And Contingencies [Line Items]
Beginning balance	15
Accruals
Payments
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
Payments
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
Payments
Ending balance	1
Less amounts in Other current liabilities	1
Amounts in Other deferred credits
Legacy Generation Regulated [Member]
Commitments And Contingencies [Line Items]
Beginning balance	7
Accruals
Payments	1
Ending balance	6
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	5
Legacy Generation Regulated [Member] | Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	3
Accruals
Payments
Ending balance	3
Less amounts in Other current liabilities
Amounts in Other deferred credits	3
Legacy Generation Regulated [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	3
Accruals
Payments	1
Ending balance	2
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	1
Legacy Generation Regulated [Member] | Atlantic City Electric Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	1
Accruals
Payments
Ending balance	1
Less amounts in Other current liabilities
Amounts in Other deferred credits	1
Legacy Generation Non-Regulated [Member]
Commitments And Contingencies [Line Items]
Beginning balance	5
Accruals
Payments
Ending balance	5
Less amounts in Other current liabilities
Amounts in Other deferred credits	5
Other [Member]
Commitments And Contingencies [Line Items]
Beginning balance	2
Accruals
Payments
Ending balance	2
Less amounts in Other current liabilities	2
Amounts in Other deferred credits
Other [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	2
Accruals
Payments
Ending balance	2
Less amounts in Other current liabilities	2
Amounts in Other deferred credits