Income Taxes - Reconciliation of Effective Income Tax Rate From Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	$ 25		$ 29	$ (79)	$ 53
State income taxes, net of Federal effect	6		5	10	10
Asset removal costs	(3)		(4)	(6)	(7)
Change in estimates and interest related to uncertain and effectively settled tax positions	3		3	70	(10)
Cross-border energy lease investments	6		(1)	70	(2)
Establishment of valuation allowances related to deferred tax assets		101		101
Other, net	(5)		(3)	1	(6)
Consolidated income tax expense	32		29	167	38
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of federal effect	8.60%		6.10%	(4.40%)	6.60%
Asset removal costs	(4.30%)		(4.90%)	2.70%	(4.60%)
Change in estimates and interest related to uncertain and effectively settled tax positions	4.30%		3.70%	(31.10%)	(6.60%)
Cross-border energy lease investments	8.60%		(1.20%)	(31.10%)	(1.30%)
Establishment of valuation allowances related to deferred tax assets				(44.90%)
Other, net	(6.50%)		(3.30%)	(0.40%)	(3.90%)
Consolidated income tax expense related to continuing operations	45.70%		35.40%	(74.20%)	25.20%
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	20		12	29	19
State income taxes, net of Federal effect	3		2	5	3
Asset removal costs	(3)		(4)	(6)	(7)
Change in estimates and interest related to uncertain and effectively settled tax positions	1		(1)	(4)	(11)
Other, net	(1)		(1)	(2)	(1)
Consolidated income tax expense	20		8	22	3
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of federal effect	5.30%		5.60%	6.10%	5.70%
Asset removal costs	(5.30%)		(11.50%)	(7.30%)	(12.80%)
Change in estimates and interest related to uncertain and effectively settled tax positions	1.80%		(3.50%)	(4.90%)	(20.20%)
Other, net	(1.70%)		(2.70%)	(2.10%)	(2.10%)
Consolidated income tax expense related to continuing operations	35.10%		22.90%	26.80%	5.60%
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	7		8	22	20
State income taxes, net of Federal effect	1		1	3	3
Change in estimates and interest related to uncertain and effectively settled tax positions				(1)
Other, net	1			1
Consolidated income tax expense	9		9	25	23
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of federal effect	4.80%		5.10%	4.80%	5.40%
Change in estimates and interest related to uncertain and effectively settled tax positions				(1.60%)	(0.20%)
Other, net	3.10%		0.80%	1.50%	0.20%
Consolidated income tax expense related to continuing operations	42.90%		40.90%	39.70%	40.40%
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	4		8	6	8
State income taxes, net of Federal effect	1		1	1	1
Change in estimates and interest related to uncertain and effectively settled tax positions	1			(9)	(1)
Other, net	(2)			3
Consolidated income tax expense	$ 4		$ 9	$ 1	$ 8
Income tax at Federal statutory rate	35.00%		35.00%	35.00%	35.00%
State income taxes, net of federal effect	9.10%		4.20%	5.90%	4.00%
Change in estimates and interest related to uncertain and effectively settled tax positions	9.10%		0.80%	(52.90%)	(4.00%)
Other, net	(16.80%)		(0.90%)	17.90%	(1.70%)
Consolidated income tax expense related to continuing operations	36.40%		39.10%	5.90%	33.30%