Income Taxes - Reconciliation of Effective Income Tax Rates From Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	$ 61		$ 51	$ 116	$ 97
State income taxes, net of Federal effect	11		9	21	19
Asset removal costs	(5)		(1)	(11)	(8)
Change in estimates and interest related to uncertain and effectively settled tax positions	1			55	(10)
Establishment of valuation allowances related to deferred tax assets		101		101
Other, net	(3)		(2)	(2)	(6)
Consolidated income tax expense	65		57	280	92
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of Federal effect	6.30%		6.30%	6.30%	6.90%
Asset removal costs	(2.90%)		(0.70%)	(3.30%)	(2.90%)
Change in estimates and interest related to uncertain and effectively settled tax positions	0.60%			16.60%	(3.60%)
Establishment of valuation allowances related to deferred tax assets				30.40%
Other, net	(1.90%)		(1.00%)	(0.70%)	(2.10%)
Consolidated income tax expense	37.10%		39.60%	84.30%	33.30%
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	37		30	66	49
State income taxes, net of Federal effect	6		5	11	8
Asset removal costs	(5)		(1)	(11)	(8)
Change in estimates and interest related to uncertain and effectively settled tax positions				(4)	(11)
Permanent differences related to deferred compensation funding					(1)
Tax credits					(1)
Other, net	2		1		2
Consolidated income tax expense	40		35	62	38
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of Federal effect	5.70%		5.90%	5.90%	5.80%
Asset removal costs	(4.70%)		(1.20%)	(5.90%)	(5.80%)
Change in estimates and interest related to uncertain and effectively settled tax positions				(2.10%)	(7.90%)
Permanent differences related to deferred compensation funding					(0.70%)
Tax credits					(0.70%)
Other, net	1.70%		1.50%	0.10%	1.60%
Consolidated income tax expense	37.70%		41.20%	33.00%	27.30%
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	13		12	35	32
State income taxes, net of Federal effect	2		2	5	5
Adjustments to prior year taxes			(2)		(2)
Change in estimates and interest related to uncertain and effectively settled tax positions				(1)
Depreciation			(1)		(1)
Other, net	(1)
Consolidated income tax expense	14		11	39	34
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of Federal effect	5.40%		6.10%	5.00%	5.60%
Adjustments to prior year taxes			(6.10%)		(2.20%)
Change in estimates and interest related to uncertain and effectively settled tax positions				(1.00%)
Depreciation			(3.00%)		(1.10%)
Other, net	(2.60%)		1.30%		0.50%
Consolidated income tax expense	37.80%		33.30%	39.00%	37.80%
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	13		11	19	20
State income taxes, net of Federal effect	2		2	4	3
Change in estimates and interest related to uncertain and effectively settled tax positions				(9)
Other, net	(2)				(2)
Consolidated income tax expense	$ 13		$ 13	$ 14	$ 21
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of Federal effect	5.30%		6.10%	7.30%	5.30%
Change in estimates and interest related to uncertain and effectively settled tax positions				(16.40%)
Other, net	(6.10%)		(1.70%)	(0.40%)	(3.50%)
Consolidated income tax expense	34.20%		39.40%	25.50%	36.80%