Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015
Other Commitments [Line Items]
Beginning balance	$ 28
Accruals	10
Payments	(5)
Ending balance	33
Less amounts in Other Current Liabilities		$ 4
Amounts in Other Deferred Credits		29
Total accrued liabilities for environmental contingencies	28	33
Legacy Generation Regulated [Member]
Other Commitments [Line Items]
Beginning balance	6
Accruals	3
Payments	(1)
Ending balance	8
Less amounts in Other Current Liabilities		1
Amounts in Other Deferred Credits		7
Total accrued liabilities for environmental contingencies	6	8
Legacy Generation Non-Regulated [Member]
Other Commitments [Line Items]
Beginning balance	5
Accruals	0
Ending balance	5
Amounts in Other Deferred Credits		5
Total accrued liabilities for environmental contingencies	5	5
Potomac Electric Power Co [Member]
Other Commitments [Line Items]
Beginning balance	19
Accruals	7
Payments	(2)
Ending balance	24
Less amounts in Other Current Liabilities		2
Amounts in Other Deferred Credits		22
Total accrued liabilities for environmental contingencies	19	24
Potomac Electric Power Co [Member] | Legacy Generation Regulated [Member]
Other Commitments [Line Items]
Beginning balance	3
Accruals	3
Ending balance	6
Amounts in Other Deferred Credits		6
Total accrued liabilities for environmental contingencies	3	6
Delmarva Power & Light Co/De [Member]
Other Commitments [Line Items]
Beginning balance	3
Accruals	3
Payments	(3)
Ending balance	3
Less amounts in Other Current Liabilities		2
Amounts in Other Deferred Credits		1
Total accrued liabilities for environmental contingencies	3	3
Delmarva Power & Light Co/De [Member] | Legacy Generation Regulated [Member]
Other Commitments [Line Items]
Beginning balance	2
Payments	(1)
Ending balance	1
Less amounts in Other Current Liabilities		1
Total accrued liabilities for environmental contingencies	2	1
Atlantic City Electric Co [Member] | Legacy Generation Regulated [Member]
Other Commitments [Line Items]
Beginning balance	1
Accruals	0
Payments	0
Ending balance	1
Amounts in Other Deferred Credits		1
Total accrued liabilities for environmental contingencies	1	1
Transmission and Distribution [Member]
Other Commitments [Line Items]
Beginning balance	17
Accruals	7
Payments	(4)
Ending balance	20
Less amounts in Other Current Liabilities		3
Amounts in Other Deferred Credits		17
Total accrued liabilities for environmental contingencies	17	20
Transmission and Distribution [Member] | Potomac Electric Power Co [Member]
Other Commitments [Line Items]
Beginning balance	16
Accruals	4
Payments	(2)
Ending balance	18
Less amounts in Other Current Liabilities		2
Amounts in Other Deferred Credits		16
Total accrued liabilities for environmental contingencies	16	18
Transmission and Distribution [Member] | Delmarva Power & Light Co/De [Member]
Other Commitments [Line Items]
Beginning balance	1
Accruals	3
Payments	(2)
Ending balance	2
Less amounts in Other Current Liabilities		1
Amounts in Other Deferred Credits		1
Total accrued liabilities for environmental contingencies	$ 1	$ 2