Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail) (USD $)	0 Months Ended	12 Months Ended
	Dec. 04, 2013	Dec. 31, 2013
Commitments and Contingencies [Line Items]
Beginning balance		$ 29,000,000
Accruals		6,000,000
Payments	(3,000)	(5,000,000)
Ending balance		30,000,000
Less amounts in Other Current Liabilities		4,000,000
Amounts in Other Deferred Credits		26,000,000
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance		17,000,000
Accruals		5,000,000
Payments	(3,000)	(1,000,000)
Ending balance		21,000,000
Less amounts in Other Current Liabilities		2,000,000
Amounts in Other Deferred Credits		19,000,000
Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Beginning balance		6,000,000
Accruals		1,000,000
Payments		(4,000,000)
Ending balance		3,000,000
Less amounts in Other Current Liabilities		2,000,000
Amounts in Other Deferred Credits		1,000,000
Transmission and Distribution [Member]
Commitments and Contingencies [Line Items]
Beginning balance		15,000,000
Accruals		5,000,000
Payments		(1,000,000)
Ending balance		19,000,000
Less amounts in Other Current Liabilities		3,000,000
Amounts in Other Deferred Credits		16,000,000
Transmission and Distribution [Member] | Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance		14,000,000
Accruals		5,000,000
Payments		(1,000,000)
Ending balance		18,000,000
Less amounts in Other Current Liabilities		2,000,000
Amounts in Other Deferred Credits		16,000,000
Transmission and Distribution [Member] | Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Beginning balance		1,000,000
Accruals
Payments
Ending balance		1,000,000
Less amounts in Other Current Liabilities		1,000,000
Amounts in Other Deferred Credits
Legacy Generation Regulated [Member]
Commitments and Contingencies [Line Items]
Beginning balance		7,000,000
Accruals
Payments		(1,000,000)
Ending balance		6,000,000
Less amounts in Other Current Liabilities		1,000,000
Amounts in Other Deferred Credits		5,000,000
Legacy Generation Regulated [Member] | Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance		3,000,000
Accruals
Payments
Ending balance		3,000,000
Less amounts in Other Current Liabilities
Amounts in Other Deferred Credits		3,000,000
Legacy Generation Regulated [Member] | Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Beginning balance		3,000,000
Accruals
Payments		(1,000,000)
Ending balance		2,000,000
Less amounts in Other Current Liabilities		1,000,000
Amounts in Other Deferred Credits		1,000,000
Legacy Generation Regulated [Member] | Atlantic City Electric Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance		1,000,000
Accruals
Payments
Ending balance		1,000,000
Less amounts in Other Current Liabilities
Amounts in Other Deferred Credits		1,000,000
Legacy Generation Non-Regulated [Member]
Commitments and Contingencies [Line Items]
Beginning balance		5,000,000
Accruals
Payments
Ending balance		5,000,000
Less amounts in Other Current Liabilities
Amounts in Other Deferred Credits		5,000,000
Other [Member]
Commitments and Contingencies [Line Items]
Beginning balance		2,000,000
Accruals		1,000,000
Payments		(3,000,000)
Ending balance
Less amounts in Other Current Liabilities
Amounts in Other Deferred Credits
Other [Member] | Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Beginning balance		2,000,000
Accruals		1,000,000
Payments		(3,000,000)
Ending balance
Less amounts in Other Current Liabilities
Amounts in Other Deferred Credits