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 -Publisher FASB
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      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph 64

</ElementReferences>
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      <ElementDefenition>The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph 64

</ElementReferences>
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      <ShortDefinition>No definition available.</ShortDefinition>
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          <NonNumericTextHeader />
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          <hasSegments>false</hasSegments>
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      </Cells>
      <OriginalInstanceReportColumns />
      <ElementDataType>xbrli:sharesItemType</ElementDataType>
      <SimpleDataType>shares</SimpleDataType>
      <ElementDefenition>The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph A240
 -Subparagraph b(1)(a, b)

</ElementReferences>
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      </Cells>
      <OriginalInstanceReportColumns />
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      <SimpleDataType>monetary</SimpleDataType>
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 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph A240
 -Subparagraph d(1)

</ElementReferences>
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          <ShowCurrencySymbol>false</ShowCurrencySymbol>
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      </Cells>
      <OriginalInstanceReportColumns />
      <ElementDataType>xbrli:sharesItemType</ElementDataType>
      <SimpleDataType>shares</SimpleDataType>
      <ElementDefenition>The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance-sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph A240
 -Subparagraph b(1)(c)

</ElementReferences>
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      <ShortDefinition>No definition available.</ShortDefinition>
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      <IsSegmentTitle>false</IsSegmentTitle>
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      <IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow>
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      <IsReverseSign>false</IsReverseSign>
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          <ShowCurrencySymbol>true</ShowCurrencySymbol>
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          <DisplayZeroAsNone>false</DisplayZeroAsNone>
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      <OriginalInstanceReportColumns />
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    <Row>
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      </Cells>
      <OriginalInstanceReportColumns />
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      <SimpleDataType>decimal</SimpleDataType>
      <ElementDefenition>The weighted-average period remaining as of the balance-sheet date until option expiration pertaining to the outstanding stock options for all option plans in the customized range of exercise prices, which may be expressed in a variety of ways (for example, years, months).</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph A240
 -Subparagraph d(1)

</ElementReferences>
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    <Row>
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      <Label>Non-Qualified Stock Options | $ 40 - $ 60</Label>
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      <ElementName />
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      <IsBaseElement>true</IsBaseElement>
      <BalanceType>na</BalanceType>
      <PeriodType>na</PeriodType>
      <ShortDefinition>No definition available.</ShortDefinition>
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      <IsSegmentTitle>true</IsSegmentTitle>
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          <DisplayDateInUSFormat>false</DisplayDateInUSFormat>
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      </Cells>
      <OriginalInstanceReportColumns>
        <Columns>
          <LabelColumn>false</LabelColumn>
          <Id>7</Id>
          <Labels>
            <Label Id="2" Label="$ 40 - $ 60" />
            <Label Id="3" Label="1/1/2009 - 12/31/2009" />
          </Labels>
          <CurrencyCode>USD</CurrencyCode>
          <FootnoteIndexer />
          <hasSegments>true</hasSegments>
          <hasScenarios>false</hasScenarios>
          <Segments>
            <Segment>
              <IsDefaultForEntity>false</IsDefaultForEntity>
              <Name />
              <IsFromEntityGroup>false</IsFromEntityGroup>
              <ValueName>us-gaap_EmployeeStockOptionMember</ValueName>
              <ValueType>us-gaap_ScheduleOfShareBasedCompensationArrangementByShareBasedPaymentAwardAwardTypeAndPlanNameAxis</ValueType>
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            </Segment>
            <Segment>
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              <Name />
              <IsFromEntityGroup>false</IsFromEntityGroup>
              <ValueName>ceg_RangeOfExercisePrice40To60DollarsMember</ValueName>
              <ValueType>us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis</ValueType>
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              <Schema>http://xbrl.org/2006/xbrldi</Schema>
              <DimensionInfo>
                <Id>ceg_RangeOfExercisePrice40To60DollarsMember</Id>
                <dimensionId>us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis</dimensionId>
                <type>explicitMember</type>
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          </Segments>
          <Scenarios />
          <Units>
            <Unit>
              <UnitID>USDPerShare</UnitID>
              <UnitType>Divide</UnitType>
              <StandardMeasure>
                <MeasureSchema />
                <MeasureValue />
                <MeasureNamespace />
              </StandardMeasure>
              <MultiplyMeasures>
                <Measure>
                  <MeasureSchema />
                  <MeasureValue />
                  <MeasureNamespace />
                </Measure>
                <Measure>
                  <MeasureSchema />
                  <MeasureValue />
                  <MeasureNamespace />
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              </MultiplyMeasures>
              <NumeratorMeasure>
                <MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema>
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                <MeasureNamespace>iso4217</MeasureNamespace>
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              <DenominatorMeasure>
                <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
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                <MeasureNamespace>xbrli</MeasureNamespace>
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              <Scale>0</Scale>
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            <Unit>
              <UnitID>Pure</UnitID>
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              <StandardMeasure>
                <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
                <MeasureValue>pure</MeasureValue>
                <MeasureNamespace>xbrli</MeasureNamespace>
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              <MultiplyMeasures>
                <Measure>
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                  <MeasureValue />
                  <MeasureNamespace />
                </Measure>
                <Measure>
                  <MeasureSchema />
                  <MeasureValue />
                  <MeasureNamespace />
                </Measure>
              </MultiplyMeasures>
              <NumeratorMeasure>
                <MeasureSchema />
                <MeasureValue />
                <MeasureNamespace />
              </NumeratorMeasure>
              <DenominatorMeasure>
                <MeasureSchema />
                <MeasureValue />
                <MeasureNamespace />
              </DenominatorMeasure>
              <Scale>0</Scale>
            </Unit>
            <Unit>
              <UnitID>Shares</UnitID>
              <UnitType>Standard</UnitType>
              <StandardMeasure>
                <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
                <MeasureValue>shares</MeasureValue>
                <MeasureNamespace>xbrli</MeasureNamespace>
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              <MultiplyMeasures>
                <Measure>
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                <Measure>
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              <NumeratorMeasure>
                <MeasureSchema />
                <MeasureValue />
                <MeasureNamespace />
              </NumeratorMeasure>
              <DenominatorMeasure>
                <MeasureSchema />
                <MeasureValue />
                <MeasureNamespace />
              </DenominatorMeasure>
              <Scale>0</Scale>
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          </Units>
          <CurrencySymbol>$</CurrencySymbol>
        </Columns>
      </OriginalInstanceReportColumns>
      <ElementDataType />
      <SimpleDataType>na</SimpleDataType>
      <ElementDefenition>No definition available.</ElementDefenition>
      <ElementReferences>No authoritative reference available.</ElementReferences>
      <IsTotalLabel>false</IsTotalLabel>
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    <Row>
      <Id>35</Id>
      <Label>Summary of stock options outstanding by range of exercise prices</Label>
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      <ElementPrefix>us-gaap</ElementPrefix>
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      <ShortDefinition>No definition available.</ShortDefinition>
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      <OriginalInstanceReportColumns />
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      <ElementDefenition>The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph 64

</ElementReferences>
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      <ShortDefinition>No definition available.</ShortDefinition>
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      <PreferredLabelRole>terselabel</PreferredLabelRole>
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          <IsNumeric>true</IsNumeric>
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          <DisplayZeroAsNone>false</DisplayZeroAsNone>
          <NumericAmount>60</NumericAmount>
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      <ElementReferences>No authoritative reference available.</ElementReferences>
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 -Publisher FASB
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 -Publisher FASB
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 -Publisher FASB
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 -Paragraph A240
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