Income Taxes - Reconciliation of Consolidated Income Tax Expense from Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Tax Rate Reconciliation [Line Items]
Income tax at federal statutory rate	$ 34	$ 29	$ 77	$ 55
State income taxes, net of federal effect	7	6	15	10
Asset removal costs	(2)	(3)	(5)	(6)
Merger-related costs	7		7
Change in estimates and interest related to uncertain and effectively settled tax positions		3		54
Establishment of valuation allowances related to deferred tax assets				101
Other, net	(1)	(5)	(3)	1
Consolidated income tax expense related to continuing operations	45	30	91	215
Income tax at federal statutory rate, percentage	35.00%	35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage	7.10%	7.20%	6.80%	6.40%
Asset removal costs, percentage	(2.00%)	(3.60%)	(2.30%)	(3.80%)
Merger-related costs, percentage	7.10%		3.20%
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage		3.60%		34.40%
Establishment of valuation allowances related to deferred tax assets, percentage				64.30%
Other, net, percentage	(1.30%)	(6.10%)	(1.10%)	0.60%
Consolidated income tax expense related to continuing operations, percentage	45.90%	36.10%	41.60%	136.90%
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at federal statutory rate	26	20	43	29
State income taxes, net of federal effect	4	3	7	5
Asset removal costs	(2)	(3)	(5)	(6)
Change in estimates and interest related to uncertain and effectively settled tax positions		1	(1)	(4)
Other, net		(1)		(2)
Consolidated income tax expense related to continuing operations	28	20	44	22
Income tax at federal statutory rate, percentage	35.00%	35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage	5.40%	5.30%	5.70%	6.10%
Asset removal costs, percentage	(2.70%)	(5.30%)	(4.10%)	(7.30%)
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage		1.80%	(0.80%)	(4.90%)
Other, net, percentage	0.10%	(1.70%)	0.30%	(2.10%)
Consolidated income tax expense related to continuing operations, percentage	37.80%	35.10%	36.10%	26.80%
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at federal statutory rate	11	7	33	22
State income taxes, net of federal effect	2	1	5	3
Change in estimates and interest related to uncertain and effectively settled tax positions				(1)
Depreciation			(1)
Other, net		1	1	1
Consolidated income tax expense related to continuing operations	13	9	38	25
Income tax at federal statutory rate, percentage	35.00%	35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage	6.30%	4.80%	5.30%	4.80%
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage				(1.60%)
Depreciation, percentage			(1.10%)
Other, net, percentage	(0.70%)	3.10%	1.20%	1.50%
Consolidated income tax expense related to continuing operations, percentage	40.60%	42.90%	40.40%	39.70%
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at federal statutory rate	3	4	9	6
State income taxes, net of federal effect	1	1	2	1
Change in estimates and interest related to uncertain and effectively settled tax positions		1		(9)
Depreciation			(1)
Other, net		(2)		3
Consolidated income tax expense related to continuing operations	$ 4	$ 4	$ 10	$ 1
Income tax at federal statutory rate, percentage	35.00%	35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage	10.00%	9.10%	7.70%	5.90%
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage		9.10%		(52.90%)
Depreciation, percentage			(3.80%)
Other, net, percentage	(5.00%)	(16.80%)	(0.40%)	17.90%
Consolidated income tax expense related to continuing operations, percentage	40.00%	36.40%	38.50%	5.90%