Income Taxes (Reconciliation Of Effective Income Tax Rate From Continuing Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate											$ 154	$ 143	$ 52
Increases (decreases) resulting from State income taxes, net of Federal effect											21	22
Asset removal costs											(11)	(7)	(3)
Change in estimates and interest related to uncertain and effectively settled tax positions											(8)	(11)	(6)
Change in state deferred tax balances as a result of restructuring													(6)
Cross-border energy lease investments											12	16	(5)
Deferred tax basis adjustments											(1)	2	(3)
Depreciation											(1)		(3)
Investment tax credit amortization											(3)	(4)	(4)
Reversal of valuation allowances													(8)
State tax benefits related to prior years' asset dispositions												(4)
Other, net											(7)	(8)	(3)
Consolidated Income Tax Expense	14	93	[1]	35	14	6	55	54	[2]	34	156	149	11
Income tax at Federal statutory rate											35.00%	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect											4.80%	5.40%
Asset removal costs											(2.50%)	(1.70%)	(2.20%)
Change in estimates and interest related to uncertain and effectively settled tax positions											(1.80%)	(2.70%)	(4.00%)
Change in state deferred tax balances as a result of restructuring													(4.00%)
Cross-border energy lease investments											2.70%	3.90%	(3.30%)
Deferred tax basis adjustments											(0.20%)	0.50%	(2.00%)
Depreciation											(0.20%)		(2.00%)
Investment tax credit amortization											(0.70%)	(1.00%)	(2.70%)
Reversal of valuation allowances													(5.30%)
State tax benefits related to prior years' asset dispositions												(1.00%)
Other, net											(1.40%)	(2.00%)	(2.20%)
Consolidated Income Tax Expense											35.40%	36.40%	7.30%
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate											61	47	51
Increases (decreases) resulting from State income taxes, net of Federal effect											10	8	8
Asset removal costs											(11)	(7)	(3)
Change in estimates and interest related to uncertain and effectively settled tax positions											(11)	(9)	(11)
Depreciation											1	(1)	3
Investment tax credit amortization											(1)	(2)	(2)
Software amortization											1		(4)
Other, net											(2)		(5)
Consolidated Income Tax Expense											48	36	37
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%	5.50%	5.50%
Asset removal costs											(6.30%)	(5.00%)	(2.10%)
Change in estimates and interest related to uncertain and effectively settled tax positions											(6.30%)	(6.60%)	(7.60%)
Depreciation											0.60%	(0.70%)	2.10%
Investment tax credit amortization											(0.60%)	(1.10%)	(1.40%)
Software amortization											0.60%	(0.30%)	(2.80%)
Other, net											(1.10%)	(0.10%)	(3.20%)
Consolidated Income Tax Expense											27.60%	26.70%	25.50%
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate											41	40	27
Increases (decreases) resulting from State income taxes, net of Federal effect											6	6	4
Change in estimates and interest related to uncertain and effectively settled tax positions												(3)	1
Deferred tax basis adjustments											(1)	(1)
Depreciation											(1)	1	1
Investment tax credit amortization											(1)	(1)	(1)
Other, net													(1)
Consolidated Income Tax Expense											44	42	31
Income tax at Federal statutory rate											35.00%	35.00%	35.00%
Increases (decreases) resulting from State income taxes, net of Federal effect											5.10%	5.30%	5.30%
Change in estimates and interest related to uncertain and effectively settled tax positions												(2.70%)	1.30%
Deferred tax basis adjustments											(0.80%)	(0.90%)
Depreciation											(0.80%)	0.90%	1.30%
Investment tax credit amortization											(0.90%)	(0.90%)	(1.30%)
Other, net												0.50%	(0.80%)
Consolidated Income Tax Expense											37.60%	37.20%	40.80%
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate											19	25	33
Increases (decreases) resulting from State income taxes, net of Federal effect											3	4	7
Adjustments to prior years' taxes												(1)
Change in estimates and interest related to uncertain and effectively settled tax positions											(1)	5	5
Depreciation											1
Investment tax credit amortization											(1)	(1)	(1)
Other, net											(2)	1	(1)
Consolidated Income Tax Expense											$ 18	$ 33	$ 43
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%	6.00%	7.30%
Adjustments to prior years' taxes												(1.70%)
Change in estimates and interest related to uncertain and effectively settled tax positions											(1.90%)	6.90%	5.20%
Investment tax credit amortization											(1.90%)	(1.30%)	(1.00%)
Other, net											(2.90%)	0.90%	(1.70%)
Consolidated Income Tax Expense											34.00%	45.80%	44.80%

[1] Includes a $16 million charge related to the recognition of the tax consequences associated with the early termination of cross-border energy leases.

[2] Includes tax benefits of $14 million in the second quarter primarily associated with an interest benefit related to federal tax liabilities and a $22 million charge related to the recognition of the tax consequences associated with the early termination of cross-border energy leases.