Regulatory Matters - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 2,246	$ 2,409
Regulatory Liabilities	308	343
Pension and Other Postretirement Benefit Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	910	946
Securitized Stranded Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	202	278
Recoverable Income Taxes [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	224	274
Demand-Side Management Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	403	329
Smart Grid Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	266	261
Deferred Energy Supply Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	32	73
Incremental Storm Restoration Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	43	51
Deferred Debt Extinguishment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	36	42
MAPP Abandonment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	7	33
Recoverable Workers' Compensation and Long-Term Disability Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	31	30
Deferred Losses on Gas Derivatives [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	2	4
Other Regulatory Assets [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	90	88
Asset Removal Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	211	250
Deferred Income Taxes Due to Customers [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	12	44
Deferred Energy Supply Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	11	3
Other Regulatory Liabilities [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	29	34
Federal and State Tax Benefits, Related to Securitized Stranded Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	13	8
Reserves for FERC ROE Transmission Challenges [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	32	4
Potomac Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	720	697
Regulatory Liabilities	92	104
Potomac Electric Power Co [Member] | Recoverable Income Taxes [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	142	148
Potomac Electric Power Co [Member] | Demand-Side Management Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	292	238
Potomac Electric Power Co [Member] | Smart Grid Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	181	175
Potomac Electric Power Co [Member] | Deferred Energy Supply Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	3	3
Potomac Electric Power Co [Member] | Incremental Storm Restoration Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	19	29
Potomac Electric Power Co [Member] | Deferred Debt Extinguishment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	19	22
Potomac Electric Power Co [Member] | MAPP Abandonment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	4	19
Potomac Electric Power Co [Member] | Recoverable Workers' Compensation and Long-Term Disability Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	31	30
Potomac Electric Power Co [Member] | Other Regulatory Assets [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	29	33
Potomac Electric Power Co [Member] | Asset Removal Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	58	84
Potomac Electric Power Co [Member] | Deferred Income Taxes Due to Customers [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	6	4
Potomac Electric Power Co [Member] | Deferred Energy Supply Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	5	3
Potomac Electric Power Co [Member] | Other Regulatory Liabilities [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	10	11
Potomac Electric Power Co [Member] | Reserves for FERC ROE Transmission Challenges [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	13	2
Delmarva Power & Light Co/De [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	308	356
Regulatory Liabilities	189	225
Delmarva Power & Light Co/De [Member] | Recoverable Income Taxes [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	38	84
Delmarva Power & Light Co/De [Member] | Demand-Side Management Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	111	91
Delmarva Power & Light Co/De [Member] | Smart Grid Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	85	86
Delmarva Power & Light Co/De [Member] | Deferred Energy Supply Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	2	12
Delmarva Power & Light Co/De [Member] | Incremental Storm Restoration Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	6	7
Delmarva Power & Light Co/De [Member] | Deferred Debt Extinguishment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	10	12
Delmarva Power & Light Co/De [Member] | MAPP Abandonment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	3	14
Delmarva Power & Light Co/De [Member] | Deferred Losses on Gas Derivatives [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	2	4
Delmarva Power & Light Co/De [Member] | Other Regulatory Assets [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	38	28
Delmarva Power & Light Co/De [Member] | COPCO Acquisition Adjustment [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	13	18
Delmarva Power & Light Co/De [Member] | Asset Removal Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	153	166
Delmarva Power & Light Co/De [Member] | Deferred Income Taxes Due to Customers [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	3	37
Delmarva Power & Light Co/De [Member] | Deferred Energy Supply Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	6
Delmarva Power & Light Co/De [Member] | Other Regulatory Liabilities [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	16	21
Delmarva Power & Light Co/De [Member] | Reserves for FERC ROE Transmission Challenges [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	11	1
Atlantic City Electric Co [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	322	427
Regulatory Liabilities	27	14
Atlantic City Electric Co [Member] | Securitized Stranded Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	202	278
Atlantic City Electric Co [Member] | Recoverable Income Taxes [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	44	42
Atlantic City Electric Co [Member] | Deferred Energy Supply Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	27	58
Atlantic City Electric Co [Member] | Incremental Storm Restoration Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	18	15
Atlantic City Electric Co [Member] | Deferred Debt Extinguishment Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	7	8
Atlantic City Electric Co [Member] | Other Regulatory Assets [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory assets	24	26
Atlantic City Electric Co [Member] | Deferred Income Taxes Due to Customers [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	3	3
Atlantic City Electric Co [Member] | Other Regulatory Liabilities [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	3	2
Atlantic City Electric Co [Member] | Federal and State Tax Benefits, Related to Securitized Stranded Costs [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	13	8
Atlantic City Electric Co [Member] | Reserves for FERC ROE Transmission Challenges [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 8	$ 1