Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies [Line Items]
Beginning balance	$ 29
Accruals	5
Payments	4
Ending balance	30
Less amounts in Other Current Liabilities	4
Amounts in Other deferred credits	26
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance	17
Accruals	4
Payments	1
Ending balance	20
Less amounts in Other Current Liabilities	2
Amounts in Other deferred credits	18
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	2
Amounts in Other deferred credits	2
Transmission and Distribution [Member]
Commitments and Contingencies [Line Items]
Beginning balance	15
Accruals	4
Payments	1
Ending balance	18
Less amounts in Other Current Liabilities	3
Amounts in Other deferred credits	15
Transmission and Distribution [Member] | Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance	14
Accruals	4
Payments	1
Ending balance	17
Less amounts in Other Current Liabilities	2
Amounts in Other deferred credits	15
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
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
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
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
Amounts in Other deferred credits	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
Amounts in Other deferred credits	$ 1