<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.3.0.814</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>636</ContextCount>
  <ElementCount>411</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>85</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>12</UnitCount>
  <MyReports>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>101 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DocumentandEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>103 - Statement - Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/StatementOfIncomeAlternative</Role>
      <ShortName>Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>104 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/StatementOfOtherComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>105 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/StatementOfFinancialPositionClassified</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>106 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/StatementOfFinancialPositionClassifiedParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>107 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/StatementOfCashFlowsIndirect</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>108 - Statement - Consolidated Statements of Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/StatementOfShareholdersEquityAndOtherComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>109 - Statement - Consolidated Statements of Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/StatementOfShareholdersEquityAndOtherComprehensiveIncomeParenthetical</Role>
      <ShortName>Consolidated Statements of Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>110 - Disclosure - Organization</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsOrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock</Role>
      <ShortName>Organization</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>111 - Disclosure - Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock</Role>
      <ShortName>Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>112 - Disclosure - Newly Adopted Accounting Standards</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock</Role>
      <ShortName>Newly Adopted Accounting Standards</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>113 - Disclosure - Recently Issued Accounting Standards, Not Yet Adopted</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsDescriptionOfNewAccountingPronouncementsNotYetAdopted</Role>
      <ShortName>Recently Issued Accounting Standards, Not Yet Adopted</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>114 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsSegmentReportingDisclosureTextBlock</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>115 - Disclosure - Goodwill</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsGoodwillDisclosureTextBlock</Role>
      <ShortName>Goodwill</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>116 - Disclosure - Regulatory Matters</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock</Role>
      <ShortName>Regulatory Matters</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>117 - Disclosure - Pension and Other Postretirement Benefits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsPensionAndOtherPostretirementBenefitsDisclosureTextBlock</Role>
      <ShortName>Pension and Other Postretirement Benefits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>118 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsDebtDisclosureTextBlock</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>119 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlock</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>120 - Disclosure - Equity and Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsEarningsPerShareTextBlock</Role>
      <ShortName>Equity and Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>121 - Disclosure - Preferred Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsPreferredStockTextBlock</Role>
      <ShortName>Preferred Stock</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>122 - Disclosure - Derivative Instruments and Hedging Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsDerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock</Role>
      <ShortName>Derivative Instruments and Hedging Activities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>123 - Disclosure - Fair Value Disclosures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsFairValueDisclosuresTextBlock</Role>
      <ShortName>Fair Value Disclosures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>124 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsCommitmentsAndContingenciesDisclosureTextBlock</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>125 - Disclosure - Variable Interest Entities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsVariableInterestEntityDisclosureTextBlock</Role>
      <ShortName>Variable Interest Entities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>126 - Disclosure - Accumulated Other Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsComprehensiveIncomeNoteTextBlock</Role>
      <ShortName>Accumulated Other Comprehensive Loss</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>127 - Disclosure - Subsequent Event</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsSubsequentEventsTextBlock</Role>
      <ShortName>Subsequent Event</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>128 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsRelatedPartyTransactionsDisclosureTextBlock</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>129 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockPolicies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>130 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsSegmentReportingDisclosureTextBlockTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsSegmentReportingDisclosureTextBlock</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>131 - Disclosure - Pension and Other Postretirement Benefits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsPensionAndOtherPostretirementBenefitsDisclosureTextBlockTables</Role>
      <ShortName>Pension and Other Postretirement Benefits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsPensionAndOtherPostretirementBenefitsDisclosureTextBlock</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>132 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlockTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlock</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>133 - Disclosure - Equity and Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsEarningsPerShareTextBlockTables</Role>
      <ShortName>Equity and Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsEarningsPerShareTextBlock</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>134 - Disclosure - Derivative Instruments and Hedging Activities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsDerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlockTables</Role>
      <ShortName>Derivative Instruments and Hedging Activities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsDerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>135 - Disclosure - Fair Value Disclosures (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsFairValueDisclosuresTextBlockTables</Role>
      <ShortName>Fair Value Disclosures (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsFairValueDisclosuresTextBlock</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>136 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsCommitmentsAndContingenciesDisclosureTextBlockTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsCommitmentsAndContingenciesDisclosureTextBlock</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>137 - Disclosure - Accumulated Other Comprehensive Loss (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsComprehensiveIncomeNoteTextBlockTables</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsComprehensiveIncomeNoteTextBlock</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>138 - Disclosure - Related Party Transactions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsRelatedPartyTransactionsDisclosureTextBlockTables</Role>
      <ShortName>Related Party Transactions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pepcoholdings.com/taxonomy/role/NotesToFinancialStatementsRelatedPartyTransactionsDisclosureTextBlock</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>139 - Disclosure - Organization - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureOrganizationAdditionalInformation</Role>
      <ShortName>Organization - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>140 - Disclosure - Significant Accounting Policies - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureSignificantAccountingPoliciesAdditionalInformation</Role>
      <ShortName>Significant Accounting Policies - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>141 - Disclosure - Segment Information - Segment Financial Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureSegmentInformationSegmentFinancialInformation</Role>
      <ShortName>Segment Information - Segment Financial Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>142 - Disclosure - Segment Information - Segment Financial Information (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureSegmentInformationSegmentFinancialInformationParenthetical</Role>
      <ShortName>Segment Information - Segment Financial Information (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>143 - Disclosure - Goodwill - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureGoodwillAdditionalInformation</Role>
      <ShortName>Goodwill - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>144 - Disclosure - Regulatory Matters - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureRegulatoryMattersAdditionalInformation</Role>
      <ShortName>Regulatory Matters - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>145 - Disclosure - Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosurePensionAndOtherPostretirementBenefitsComponentsOfNetPeriodicBenefitCosts</Role>
      <ShortName>Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>146 - Disclosure - Pension and Other Postretirement Benefits - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosurePensionAndOtherPostretirementBenefitsAdditionalInformation</Role>
      <ShortName>Pension and Other Postretirement Benefits - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>147 - Disclosure - Debt - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureDebtAdditionalInformation</Role>
      <ShortName>Debt - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>148 - Disclosure - Income Taxes - Reconciliation of Consolidated Income Tax Expense (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureIncomeTaxesReconciliationOfConsolidatedIncomeTaxExpense</Role>
      <ShortName>Income Taxes - Reconciliation of Consolidated Income Tax Expense (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>149 - Disclosure - Income Taxes - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureIncomeTaxesAdditionalInformation</Role>
      <ShortName>Income Taxes - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>150 - Disclosure - Equity and Earnings Per Share - Calculation of Earnings Per Share of Common Stock (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureEquityAndEarningsPerShareCalculationOfEarningsPerShareOfCommonStock</Role>
      <ShortName>Equity and Earnings Per Share - Calculation of Earnings Per Share of Common Stock (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>151 - Disclosure - Equity and Earnings Per Share - Calculation of Earnings Per Share of Common Stock (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureEquityAndEarningsPerShareCalculationOfEarningsPerShareOfCommonStockParenthetical</Role>
      <ShortName>Equity and Earnings Per Share - Calculation of Earnings Per Share of Common Stock (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>152 - Disclosure - Preferred Stock - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosurePreferredStockAdditionalInformation</Role>
      <ShortName>Preferred Stock - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>153 - Disclosure - Derivative Instruments and Hedging Activities - Fair Values of Derivative Instruments by Balance Sheet Location (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureDerivativeInstrumentsAndHedgingActivitiesFairValuesOfDerivativeInstrumentsByBalanceSheetLocation</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Fair Values of Derivative Instruments by Balance Sheet Location (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>154 - Disclosure - Derivative Instruments and Hedging Activities - Schedule of Cash Collateral Offset Against Derivative Positions (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureDerivativeInstrumentsAndHedgingActivitiesScheduleOfCashCollateralOffsetAgainstDerivativePositions</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Schedule of Cash Collateral Offset Against Derivative Positions (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>155 - Disclosure - Derivative Instruments and Hedging Activities - Cash Flow Hedges Included in Accumulated Other Comprehensive Loss (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureDerivativeInstrumentsAndHedgingActivitiesCashFlowHedgesIncludedInAccumulatedOtherComprehensiveLoss</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Cash Flow Hedges Included in Accumulated Other Comprehensive Loss (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>156 - Disclosure - Derivative Instruments and Hedging Activities - Net Unrealized and Realized Derivative Gains (Losses) Deferred as Regulatory Liabilities and Regulatory Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureDerivativeInstrumentsAndHedgingActivitiesNetUnrealizedAndRealizedDerivativeGainsLossesDeferredAsRegulatoryLiabilitiesAndRegulatoryAssets</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Net Unrealized and Realized Derivative Gains (Losses) Deferred as Regulatory Liabilities and Regulatory Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>157 - Disclosure - Derivative Instruments and Hedging Activities - Net Outstanding Commodity Forward Contracts That Did Not Qualify For Hedge Accounting (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureDerivativeInstrumentsAndHedgingActivitiesNetOutstandingCommodityForwardContractsThatDidNotQualifyForHedgeAccounting</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Net Outstanding Commodity Forward Contracts That Did Not Qualify For Hedge Accounting (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>158 - Disclosure - Fair Value Disclosures - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureFairValueDisclosuresFairValueOfFinancialAssetsAndLiabilitiesMeasuredOnRecurringBasis</Role>
      <ShortName>Fair Value Disclosures - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>159 - Disclosure - Fair Value Disclosures - Reconciliations of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureFairValueDisclosuresReconciliationsOfFairValueMeasurementsUsingSignificantUnobservableInputsLevel3</Role>
      <ShortName>Fair Value Disclosures - Reconciliations of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>160 - Disclosure - Fair Value Disclosures - Gains on Level 3 Instruments Included in Income (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureFairValueDisclosuresGainsOnLevel3InstrumentsIncludedInIncome</Role>
      <ShortName>Fair Value Disclosures - Gains on Level 3 Instruments Included in Income (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>161 - Disclosure - Fair Value Disclosures - Fair Value of Financial Liabilities Measured on Recurring Basis (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureFairValueDisclosuresFairValueOfFinancialLiabilitiesMeasuredOnRecurringBasis</Role>
      <ShortName>Fair Value Disclosures - Fair Value of Financial Liabilities Measured on Recurring Basis (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>162 - Disclosure - Fair Value Disclosures - Fair Value of Financial Liabilities Measured on Recurring Basis (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureFairValueDisclosuresFairValueOfFinancialLiabilitiesMeasuredOnRecurringBasisParenthetical</Role>
      <ShortName>Fair Value Disclosures - Fair Value of Financial Liabilities Measured on Recurring Basis (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>163 - Disclosure - Commitments and Contingencies - Retained Environmental Exposures - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureCommitmentsAndContingenciesRetainedEnvironmentalExposuresAdditionalInformation</Role>
      <ShortName>Commitments and Contingencies - Retained Environmental Exposures - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>164 - Disclosure - Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfAccruedLiabilitiesForEnvironmentalExposures</Role>
      <ShortName>Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>165 - Disclosure - Commitments and Contingencies - Environmental Matters - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureCommitmentsAndContingenciesEnvironmentalMattersAdditionalInformation</Role>
      <ShortName>Commitments and Contingencies - Environmental Matters - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>166 - Disclosure - Commitments and Contingencies - Schedule of Commitments and Obligations (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfCommitmentsAndObligations</Role>
      <ShortName>Commitments and Contingencies - Schedule of Commitments and Obligations (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>167 - Disclosure - Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfCommitmentsAndObligationsParenthetical</Role>
      <ShortName>Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>168 - Disclosure - Commitments and Contingencies - Tax Legislation, Guarantees, Indemnifications, and Performance Contracts - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureCommitmentsAndContingenciesTaxLegislationGuaranteesIndemnificationsAndPerformanceContractsAdditionalInformation</Role>
      <ShortName>Commitments and Contingencies - Tax Legislation, Guarantees, Indemnifications, and Performance Contracts - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>169 - Disclosure - Variable Interest Entities - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureVariableInterestEntitiesAdditionalInformation</Role>
      <ShortName>Variable Interest Entities - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>170 - Disclosure - Accumulated Other Comprehensive Loss - Schedule of Components of Other Comprehensive Loss (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureAccumulatedOtherComprehensiveLossScheduleOfComponentsOfOtherComprehensiveLoss</Role>
      <ShortName>Accumulated Other Comprehensive Loss - Schedule of Components of Other Comprehensive Loss (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>171 - Disclosure - Subsequent Event - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureSubsequentEventAdditionalInformation</Role>
      <ShortName>Subsequent Event - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>172 - Disclosure - Segment Information - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureSegmentInformationAdditionalInformation</Role>
      <ShortName>Segment Information - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>173 - Disclosure - Related Party Transactions - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformation</Role>
      <ShortName>Related Party Transactions - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>174 - Disclosure - Related Party Transactions - Schedule of Related Party Transactions Included in Balance Sheet (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureRelatedPartyTransactionsScheduleOfRelatedPartyTransactionsIncludedInBalanceSheet</Role>
      <ShortName>Related Party Transactions - Schedule of Related Party Transactions Included in Balance Sheet (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="pom-20150930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>175 - Disclosure - Related Party Transactions - Schedule of Related Party Transactions Included in Income Statement (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pepcoholdings.com/taxonomy/role/DisclosureRelatedPartyTransactionsScheduleOfRelatedPartyTransactionsIncludedInIncomeStatement</Role>
      <ShortName>Related Party Transactions - Schedule of Related Party Transactions Included in Income Statement (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">In ''Consolidated Statements of Income'', column(s) 4, 5 are contained in other reports, so were removed by flow through suppression.</Log>
    <Log type="Info">In ''Consolidated Statements of Comprehensive Income'', column(s) 2, 3 are contained in other reports, so were removed by flow through suppression.</Log>
    <Log type="Info">In ''Consolidated Balance Sheets'', column(s) 2, 3, 5, 6, 7 are contained in other reports, so were removed by flow through suppression.</Log>
    <Log type="Info">In ''Consolidated Balance Sheets (Parenthetical)'', column(s) 7 are contained in other reports, so were removed by flow through suppression.</Log>
    <Log type="Info">In ''Consolidated Statements of Cash Flows'', column(s) 1, 2, 3, 4 are contained in other reports, so were removed by flow through suppression.</Log>
  </Logs>
  <InputFiles>
    <File>pom-20150930.xml</File>
    <File>pom-20150930_cal.xml</File>
    <File>pom-20150930_def.xml</File>
    <File>pom-20150930_lab.xml</File>
    <File>pom-20150930_pre.xml</File>
    <File>pom-20150930.xsd</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>

