Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended		6 Months Ended
	Nov. 01, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Significant Accounting Policies [Line Items]
Estimated fair value of an asset	Greater than 50%
Taxes included in gross revenues		$ 78	$ 83	$ 161	$ 166
Prior period item reclassification adjustment in Net cash used by operating activities					35
Prior period item reclassification adjustment change in Net cash used by operating activities					12
Net Cash From (Used By) Operating Activities					47
Prior period item reclassification adjustment in cash from financing activities					58
Prior period item reclassification adjustment Change in cash from financing activities					12
Net Cash From Financing Activities					46
Potomac Electric Power Co [Member]
Significant Accounting Policies [Line Items]
Taxes included in gross revenues		74	77	152	153
Prior period item reclassification adjustment in Net cash used by operating activities					84
Prior period item reclassification adjustment change in Net cash used by operating activities					5
Net Cash From (Used By) Operating Activities					79
Prior period item reclassification adjustment in cash from financing activities					166
Prior period item reclassification adjustment Change in cash from financing activities					5
Net Cash From Financing Activities					171
Delmarva Power & Light Co/De [Member]
Significant Accounting Policies [Line Items]
Estimated fair value of an asset	Greater than 50%
Taxes included in gross revenues		4	4	8	8
Prior period item reclassification adjustment in Net cash used by operating activities					105
Prior period item reclassification adjustment change in Net cash used by operating activities					2
Net Cash From (Used By) Operating Activities					103
Prior period item reclassification adjustment in cash from financing activities					55
Prior period item reclassification adjustment Change in cash from financing activities					2
Net Cash From Financing Activities					57
Atlantic City Electric Co [Member]
Significant Accounting Policies [Line Items]
Taxes included in gross revenues		0	2	1	5
Prior period item reclassification adjustment in Net cash used by operating activities					49
Prior period item reclassification adjustment change in Net cash used by operating activities					1
Net Cash From (Used By) Operating Activities					48
Prior period item reclassification adjustment in cash from financing activities					87
Prior period item reclassification adjustment Change in cash from financing activities					1
Net Cash From Financing Activities					88
Adjustment [Member]
Significant Accounting Policies [Line Items]
Deferred income tax liabilities			$ 32