Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Commitments And Contingencies [Line Items]
Beginning balance	$ 29
Accruals	3
Payments	4
Ending balance	28
Less amounts in Other current liabilities	4
Amounts in Other deferred credits	24
Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	17
Accruals	2
Payments	1
Ending balance	18
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	17
Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	6
Accruals	1
Payments	3
Ending balance	4
Less amounts in Other current liabilities	3
Amounts in Other deferred credits	1
Transmission And Distribution [Member]
Commitments And Contingencies [Line Items]
Beginning balance	15
Accruals	2
Payments	1
Ending balance	16
Less amounts in Other current liabilities	2
Amounts in Other deferred credits	14
Transmission And Distribution [Member] | Potomac Electric Power Co [Member]
Commitments And Contingencies [Line Items]
Beginning balance	14
Accruals	2
Payments	1
Ending balance	15
Less amounts in Other current liabilities	1
Amounts in Other deferred credits	14
Transmission And Distribution [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	1
Ending balance	1
Less amounts in Other current liabilities	1
Legacy Generation Regulated [Member]
Commitments And Contingencies [Line Items]
Beginning balance	7
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
Ending balance	3
Amounts in Other deferred credits	3
Legacy Generation Regulated [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	3
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
Ending balance	5
Amounts in Other deferred credits	5
Other [Member]
Commitments And Contingencies [Line Items]
Beginning balance	2
Accruals	1
Payments	2
Ending balance	1
Less amounts in Other current liabilities	1
Other [Member] | Delmarva Power & Light Co/De [Member]
Commitments And Contingencies [Line Items]
Beginning balance	2
Accruals	1
Payments	2
Ending balance	1
Less amounts in Other current liabilities	$ 1