Income Taxes - Reconciliation of Consolidated Income Tax Expense from Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	$ 42	$ 26
Increases (decreases) resulting from State income taxes, net of Federal effect	7	5
Asset removal costs	(2)	(3)
Change in estimates and interest related to uncertain and effectively settled tax positions	(1)	51
Establishment of valuation allowances related to deferred tax assets		101
Other, net		5
Consolidated income tax expense related to continuing operations	46	185
Income tax at Federal statutory rate	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect	5.80%	6.80%
Asset removal costs	(1.70%)	(4.10%)
Change in estimates and interest related to uncertain and effectively settled tax positions	(0.80%)	68.90%
Establishment of valuation allowances related to deferred tax assets		136.50%
Other, net	(0.30%)	6.90%
Consolidated income tax expense (benefit)	38.00%	250.00%
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	22	15
Increases (decreases) resulting from State income taxes, net of Federal effect	3	2
Change in estimates and interest related to uncertain and effectively settled tax positions		(1)
Other, net
Consolidated income tax expense related to continuing operations	25	16
Income tax at Federal statutory rate	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect	4.80%	4.70%
Change in estimates and interest related to uncertain and effectively settled tax positions		(2.40%)
Other, net	0.50%	0.80%
Consolidated income tax expense (benefit)	40.30%	38.10%
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	17	9
Increases (decreases) resulting from State income taxes, net of Federal effect	3	2
Asset removal costs	(2)	(3)
Change in estimates and interest related to uncertain and effectively settled tax positions	(1)	(5)
Other, net	(1)	(1)
Consolidated income tax expense related to continuing operations	16	2
Income tax at Federal statutory rate	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect	6.30%	8.00%
Asset removal costs	(4.20%)	(12.00%)
Change in estimates and interest related to uncertain and effectively settled tax positions	(2.10%)	(20.00%)
Other, net	(1.70%)	(3.00%)
Consolidated income tax expense (benefit)	33.30%	8.00%
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	6	2
Increases (decreases) resulting from State income taxes, net of Federal effect		1
Adjustments to prior year taxes		4
Change in estimates and interest related to uncertain and effectively settled tax positions		(10)
Other, net
Consolidated income tax expense related to continuing operations	$ 6	$ (3)
Income tax at Federal statutory rate	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect		16.80%
Adjustments to prior year taxes		65.60%
Change in estimates and interest related to uncertain and effectively settled tax positions		(167.70%)
Other, net	2.50%
Consolidated income tax expense (benefit)	37.50%	(50.30%)