Income Taxes - Components of Consolidated Deferred Tax Liabilities (Assets) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Depreciation and other basis differences related to plant and equipment	$ 2,628	$ 2,299
Deferred electric service and electric restructuring liabilities	91	110
Cross-border energy lease investments	(6)	756
Federal and state net operating loss	(350)	(394)
Valuation allowances on state net operating losses	21	21
Pension and other postretirement benefits	135	128
Deferred taxes on amounts to be collected through future rates	75	58
Other	285	204
Total Deferred Tax Liabilities, net	2,879	3,182
Deferred tax assets included in Current Assets	51	28
Deferred tax liabilities included in Other Current Liabilities	(2)	(2)
Total Consolidated Deferred Tax Liabilities, net non-current	2,928	3,208
Potomac Electric Power Co [Member]
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Depreciation and other basis differences related to plant and equipment	1,240	1,105
Federal and state net operating loss	(169)	(174)
Pension and other postretirement benefits	105	111
Deferred taxes on amounts to be collected through future rates	43	28
Other	145	140
Total Deferred Tax Liabilities, net	1,364	1,210
Deferred tax assets included in Current Assets	48	9
Total Consolidated Deferred Tax Liabilities, net non-current	1,412	1,219
Delmarva Power & Light Co/De [Member]
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Depreciation and other basis differences related to plant and equipment	712	623
Deferred electric service and electric restructuring liabilities	(5)	(5)
Federal and state net operating loss	(125)	(80)
Pension and other postretirement benefits	80	85
Deferred taxes on amounts to be collected through future rates	16	15
Other	80	49
Total Deferred Tax Liabilities, net	758	687
Deferred tax assets included in Current Assets	59	11
Deferred tax liabilities included in Other Current Liabilities	(1)	(1)
Total Consolidated Deferred Tax Liabilities, net non-current	816	697
Atlantic City Electric Co [Member]
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Depreciation and other basis differences related to plant and equipment	627	538
Deferred electric service and electric restructuring liabilities	96	116
Federal and state net operating loss	(49)	(54)
Pension and other postretirement benefits	29	34
Deferred taxes on amounts to be collected through future rates	16	15
Payment for termination of purchased power contracts with NUGs	43	47
Purchased energy	2	3
Other	55	58
Total Deferred Tax Liabilities, net	819	757
Deferred tax assets included in Current Assets	15	10
Deferred tax liabilities included in Other Current Liabilities	(1)	(1)
Total Consolidated Deferred Tax Liabilities, net non-current	$ 833	$ 766