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Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Derivative [Line Items] |  |  |
Cash collateral held |  | $ 17 |
Letters of credit held |  | 35 |
Exelon Generation Co L L C [Member] |  |  |
Derivative [Line Items] |  |  |
Cash collateral held |  | 47 | $ 35
Letters of credit held |  | 44 | $ 33
Total Exposure Before Credit Collateral [Member] | Exelon Generation Co L L C [Member] |  |  |
Derivative [Line Items] |  |  |
Investment grade |  | 795 |
Non-investment grade |  | 133 |
Internally rated — investment grade |  | 181 |
Internally rated — non-investment grade |  | 92 |
Total |  | 1,201 |
Credit Collateral [Member] | Exelon Generation Co L L C [Member] |  |  |
Derivative [Line Items] |  |  |
Investment grade |  | 0 |
Non-investment grade |  | 45 |
Internally rated — investment grade |  | 1 |
Internally rated — non-investment grade |  | 6 |
Total | [1] | 52 |
Net Exposure [Member] | Exelon Generation Co L L C [Member] |  |  |
Derivative [Line Items] |  |  |
Investment grade |  | 795 |
Non-investment grade |  | 88 |
Internally rated — investment grade |  | 180 |
Internally rated — non-investment grade |  | 86 |
Total |  | 1,149 |
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] | Exelon Generation Co L L C [Member] |  |  |
Derivative [Line Items] |  |  |
Investment grade |  | 1 |
Non-investment grade |  | 0 |
Internally rated — investment grade |  | 0 |
Internally rated — non-investment grade |  | 0 |
Total |  | 1 |
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] | Exelon Generation Co L L C [Member] |  |  |
Derivative [Line Items] |  |  |
Investment grade |  | 153 |
Non-investment grade |  | 0 |
Internally rated — investment grade |  | 0 |
Internally rated — non-investment grade |  | 0 |
Total |  | $ 153 |
[1] | As of December 31, 2018, credit collateral held from counterparties where Generation had credit exposure included $17 million of cash and $35 million of letters of credit. The credit collateral does not include non-liquid collateral.

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- Definition Cash collateral held related to credit risk. + References No definition available. + Details
Name: | exc_CashCollateralHeld
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) with external credit-rating that could be used to describe the current status and performance risk of derivatives and guarantee obligations that connote investment grade. + References No definition available. + Details
Name: | exc_InvestmentGradeExternalCreditRating
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) with an entity's internal risk assessment as having low risk. + References No definition available. + Details
Name: | exc_InvestmentGradeInternalCreditRating
Namespace Prefix: | exc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Letters of credit held related to credit risk + References No definition available. + Details
Name: | exc_LettersOfCreditHeld
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) with external credit-rating that could be used to describe the current status and performance risk of derivatives and guarantee obligations that connote non-investment grade. + References No definition available. + Details
Name: | exc_NonInvestmentGradeExternalCreditRating
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) with an entity's internal risk assessment as having high risk. + References No definition available. + Details
Name: | exc_NoninvestmentGradeInternalCreditRating
Namespace Prefix: | exc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Total credit risk exposure. + References No definition available. + Details
Name: | exc_TotalCreditRiskExposure
Namespace Prefix: | exc_
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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- Details
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Namespace Prefix: |
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Period Type: |

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- Details
Name: | exc_CreditRiskExposureAxis=exc_TotalExposureBeforeCreditCollateralMember
Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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- Details
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