Income Taxes - Components of Consolidated Deferred Tax Liabilities (Assets) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Depreciation and other basis differences related to plant and equipment	$ 3,273	$ 2,962
Deferred electric service and electric restructuring liabilities	43	67
Federal and state net operating losses	(446)	(400)
Valuation allowances on state net operating losses	63	61	$ 101
Pension and other postretirement benefits	92	116
Deferred taxes on amounts to be collected through future rates	86	94
Other	267	325
Total Consolidated Deferred Tax Liabilities, net	3,378	3,225
Deferred tax assets included in Other Assets	0	0
Total Consolidated Deferred Tax Liabilities, net	3,393	3,242
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	1,541	1,423
Federal and state net operating losses	(141)	(186)
Pension and other postretirement benefits	95	103
Deferred taxes on amounts to be collected through future rates	55	59
Other	171	180
Total Consolidated Deferred Tax Liabilities, net	1,721	1,579
Total Consolidated Deferred Tax Liabilities, net	1,721	1,579
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	899	797
Deferred electric service and electric restructuring liabilities	(4)	(4)
Federal and state net operating losses	(122)	(115)
Pension and other postretirement benefits	75	80
Deferred taxes on amounts to be collected through future rates	15	19
Other	78	101
Total Consolidated Deferred Tax Liabilities, net	941	878
Total Consolidated Deferred Tax Liabilities, net	941	878
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	773	691
Deferred electric service and electric restructuring liabilities	47	71
Federal and state net operating losses	(9)	(26)
Pension and other postretirement benefits	20	25
Deferred taxes on amounts to be collected through future rates	17	16
Payment for termination of purchased power contracts with NUGs	34	38
Other	6	40
Total Consolidated Deferred Tax Liabilities, net	888	855
Total Consolidated Deferred Tax Liabilities, net	$ 888	$ 855