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Derivative Financial Instruments - Net Credit Exposure by Type of Counterparty (Details) - Exelon Generation Co L L C [Member] - Net Exposure [Member] $ in Millions | Dec. 31, 2018 USD ($)
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Derivative [Line Items] |
Financial institutions | $ 12
Investor-owned utilities, marketers, power producers | 737
Energy cooperatives and municipalities | 324
Other | 76
Total | $ 1,149

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- Definition Net credit exposure from energy cooperatives and municipalities + References No definition available. + Details
Name: | exc_EnergyCooperativesAndMunicipalities
Namespace Prefix: | exc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Credit exposure for all derivative instruments, normal purchase-normal sale, and related payables and receivables (net of collateral and instruments that are subject to master netting agreements) from group of counterparties comprised of financial institutions. + References No definition available. + Details
Name: | exc_FinancialInstitutionsCreditRiskExposure
Namespace Prefix: | exc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Credit exposure for all derivative instruments, normal purchase-normal sale, and related payables and receivables (net of collateral and instruments that are subject to master netting agreements) from group of counterparties comprised of investor-owned utilities, marketers and power producers. + References No definition available. + Details
Name: | exc_InvestorOwnedUtilitiesMarketersAndPowerProducersCreditRiskExposure
Namespace Prefix: | exc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Credit exposure for all derivative instruments, normal purchase-normal sale, and related payables and receivables (net of collateral and instruments that are subject to master netting agreements) from group of counterparties not separately identified elsewhere. + References No definition available. + Details
Name: | exc_OtherCreditRiskExposure
Namespace Prefix: | exc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4K -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5708775-113959 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | dei_LegalEntityAxis=exc_ExelonGenerationCoLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | exc_CreditRiskExposureAxis=exc_NetExposureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |