Income Taxes - Reconciliation of Consolidated Income Tax Expense from Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									$ 150	$ 112	$ 118
Increases (decreases) resulting from State income taxes, net of Federal effect									27	19	23
Asset removal costs									(14)	(11)	(7)
Change in estimates and interest related to uncertain and effectively settled tax positions				56					56	(8)	(5)
Establishment of valuation allowances related to deferred tax assets				101					101
Other, net									(1)	(9)	(15)
Consolidated Income Tax Expense	39	65	30	185	11	57	26	9	319	103	114
Income tax at Federal statutory rate									35.00%	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect									6.30%	6.00%	6.70%
Asset removal costs									(3.30%)	(3.40%)	(2.10%)
Change in estimates and interest related to uncertain and effectively settled tax positions									13.10%	(2.60%)	(1.60%)
Establishment of valuation allowances related to deferred tax assets									23.50%
Other, net									(0.20%)	(2.90%)	(4.10%)
Consolidated Income Tax Expense									74.40%	32.10%	33.90%
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									80	61	47
Increases (decreases) resulting from State income taxes, net of Federal effect									13	10	8
Asset removal costs									(14)	(11)	(7)
Change in estimates and interest related to uncertain and effectively settled tax positions				5					(3)	(11)	(9)
Establishment of valuation allowances related to deferred tax assets									0	0
Other, net									3	(1)	(3)
Consolidated Income Tax Expense	17	40	20	2	10	35	8		79	48	36
Income tax at Federal statutory rate									35.00%	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect									5.70%	5.70%	5.50%
Asset removal costs									(6.10%)	(6.30%)	(5.00%)
Change in estimates and interest related to uncertain and effectively settled tax positions									(1.30%)	(6.30%)	(6.60%)
Other, net									1.20%	(0.50%)	(2.20%)
Consolidated Income Tax Expense									34.50%	27.60%	26.70%
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									51	41	40
Increases (decreases) resulting from State income taxes, net of Federal effect									8	6	6
Change in estimates and interest related to uncertain and effectively settled tax positions											(3)
Establishment of valuation allowances related to deferred tax assets									0	0
Other, net									(3)	(3)	(1)
Consolidated Income Tax Expense	17	14	9	16	10	11	9	14	56	44	42
Income tax at Federal statutory rate									35.00%	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect									5.50%	5.10%	5.30%
Change in estimates and interest related to uncertain and effectively settled tax positions											(2.70%)
Other, net									(1.90%)	(2.50%)	(0.40%)
Consolidated Income Tax Expense									38.60%	37.60%	37.20%
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									24	19	25
Increases (decreases) resulting from State income taxes, net of Federal effect									5	3	4
Change in estimates and interest related to uncertain and effectively settled tax positions									(9)	(1)	5
Establishment of valuation allowances related to deferred tax assets									0	0
Plant basis adjustments									(2)	(1)
Investment tax credit amortization									(1)	(1)	(1)
Other, net									2	(1)
Consolidated Income Tax Expense	$ 5	$ 13	$ 4	$ (3)	$ 13	$ (3)	$ 9	$ (1)	$ 19	$ 18	$ 33
Income tax at Federal statutory rate									35.00%	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect									7.20%	5.70%	6.00%
Change in estimates and interest related to uncertain and effectively settled tax positions									(13.00%)	(1.90%)	6.90%
Plant basis adjustments									(2.90%)	(1.90%)
Investment tax credit amortization									(1.40%)	(1.90%)	(1.30%)
Other, net									2.60%	(1.00%)	0.80%
Consolidated Income Tax Expense									27.50%	34.00%	45.80%