Commitments And Contingencies (Schedule Of Accrued Liabilities For Environmental Exposures) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	$ 35
Accruals
Payments	(1)
Ending balance as of June 30	34
Less amounts in Other current liabilities	6
Amounts in Other deferred credits	28
Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	18
Accruals
Payments	(1)
Ending balance as of June 30	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 as of January 1	7
Accruals
Payments	(1)
Ending balance as of June 30	6
Less amounts in Other current liabilities	4
Amounts in Other deferred credits	2
Atlantic City Electric Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	1
Accruals
Ending balance as of June 30	1
Amounts in Other deferred credits	1
Transmission And Distribution [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	15
Accruals
Ending balance as of June 30	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 as of January 1	14
Accruals
Ending balance as of June 30	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 as of January 1	1
Accruals
Ending balance as of June 30	1
Less amounts in Other current liabilities	1
Regulated Operation [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	8
Accruals
Payments	(1)
Ending balance as of June 30	7
Less amounts in Other current liabilities	2
Amounts in Other deferred credits	5
Regulated Operation [Member] | Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	4
Accruals
Payments	(1)
Ending balance as of June 30	3
Amounts in Other deferred credits	3
Regulated Operation [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	4
Accruals
Payments	(1)
Ending balance as of June 30	3
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	2
Regulated Operation [Member] | Atlantic City Electric Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	1
Accruals
Ending balance as of June 30	1
Amounts in Other deferred credits	1
Unregulated Operation [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	10
Accruals
Ending balance as of June 30	10
Amounts in Other deferred credits	10
Other Operating Expense [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	2
Accruals
Ending balance as of June 30	2
Less amounts in Other current liabilities	2
Other Operating Expense [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance as of January 1	2
Accruals
Ending balance as of June 30	2
Less amounts in Other current liabilities	$ 2