Income Taxes (Components Of Consolidated Deferred Tax Liabilities (Assets)) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred Tax Liabilities (Assets)
Depreciation and other basis differences related to plant and equipment	$ 2,299	$ 1,871
Deferred electric service and electric restructuring liabilities	110	131
Cross-border energy lease investments	756	793
Federal and state net operating losses	(394)	(220)
Valuation allowances on state net operating losses	21	21
Pension and other postretirement benefits	128	130
Deferred taxes on amounts to be collected through future rates	58	47
Other	172	32
Total Deferred Tax Liabilities, net	3,150	2,805
Deferred tax assets included in Current Assets	28	59
Deferred tax liabilities included in Other Current Liabilities	(2)	(1)
Total Consolidated Deferred Tax Liabilities, net non-current	3,176	2,863
Depreciation and other basis differences related to plant and equipment	2,299	1,871
Deferred taxes on amounts to be collected through future rates	58	47
Deferred electric service and electric restructuring liabilities	110	131
Pension and other postretirement benefits	128	130
Federal and state net operating loss	(394)	(220)
Other	172	32
Total Deferred Tax Liabilities, net	3,150	2,805
Deferred tax assets included in Current Assets	28	59
Total Consolidated Deferred Tax Liabilities, net non-current	3,176	2,863
Potomac Electric Power Co [Member]
Deferred Tax Liabilities (Assets)
Depreciation and other basis differences related to plant and equipment	1,105	902
Federal and state net operating losses	(174)	(80)
Pension and other postretirement benefits	111	117
Deferred taxes on amounts to be collected through future rates	28	20
Other	140	69
Total Deferred Tax Liabilities, net	1,210	1,028
Deferred tax assets included in Current Assets	9	11
Total Consolidated Deferred Tax Liabilities, net non-current	1,219	1,039
Depreciation and other basis differences related to plant and equipment	1,105	902
Deferred taxes on amounts to be collected through future rates	28	20
Pension and other postretirement benefits	111	117
Federal and state net operating loss	(174)	(80)
Other	140	69
Total Deferred Tax Liabilities, net	1,210	1,028
Deferred tax assets included in Current Assets	9	11
Total Consolidated Deferred Tax Liabilities, net non-current	1,219	1,039
Delmarva Power & Light Co/De [Member]
Deferred Tax Liabilities (Assets)
Depreciation and other basis differences related to plant and equipment	623	526
Deferred electric service and electric restructuring liabilities	(5)
Pension and other postretirement benefits	85	86
Deferred taxes on amounts to be collected through future rates	15	14
Federal and state net operating losses	(80)	(57)
Other	49	34
Total Deferred Tax Liabilities, net	687	603
Deferred tax assets included in Current Assets	11	11
Deferred tax liabilities included in Other Current Liabilities	(1)	1
Total Consolidated Deferred Tax Liabilities, net non-current	697	615
Depreciation and other basis differences related to plant and equipment	623	526
Deferred taxes on amounts to be collected through future rates	15	14
Deferred electric service and electric restructuring liabilities	(5)
Pension and other postretirement benefits	85	86
Other	49	34
Total Deferred Tax Liabilities, net	687	603
Deferred tax assets included in Current Assets	11	11
Total Consolidated Deferred Tax Liabilities, net non-current	697	615
Atlantic City Electric Co [Member]
Deferred Tax Liabilities (Assets)
Depreciation and other basis differences related to plant and equipment	538	424
Deferred electric service and electric restructuring liabilities	116	137
Federal and state net operating losses	(54)	(8)
Pension and other postretirement benefits	34	28
Deferred taxes on amounts to be collected through future rates	15	11
Other	58	40
Total Deferred Tax Liabilities, net	757	689
Deferred tax assets included in Current Assets	10	9
Total Consolidated Deferred Tax Liabilities, net non-current	766	698
Depreciation and other basis differences related to plant and equipment	538	424
Deferred taxes on amounts to be collected through future rates	15	11
Payment for termination of purchased power contracts with NUGs	47	53
Deferred electric service and electric restructuring liabilities	116	137
Pension and other postretirement benefits	34	28
Fuel and purchased energy	3	4
Federal and state net operating loss	(54)	(8)
Other	58	40
Total Deferred Tax Liabilities, net	757	689
Deferred tax assets included in Current Assets	10	9
Deferred tax liabilities included in Other Current Liabilities	(1)
Total Consolidated Deferred Tax Liabilities, net non-current	$ 766	$ 698