Cash Remitted To VIE

No definition available.

Name:	exc_CashRemittedToVIE
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of variable interest entities (VIEs) consolidated.

+ References

No definition available.

+ Details

Name:	exc_NumberOfVariableInterestEntitiesConsolidated
Namespace Prefix:	exc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of variable interest entities (VIEs) not consolidated.

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Project Entities with Noncontrolling Interests

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Ownership Interest in Project Entities

+ References

No definition available.

+ Details

Name:	exc_OwnershipInterestinProjectEntities
Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of ownership interest in certain nonconsolidated VIEs where none of the equity holders consolidate these VIEs.

+ References

No definition available.

+ Details

Name:	exc_OwnershipPercentageOfConsolidatedVariableInterestEntities
Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Ownership Percentage of Noncontrolling Interests in Project Entities

+ References

No definition available.

+ Details

Name:	exc_OwnershipPercentageofNoncontrollingInterestsinProjectEntities
Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Projects with economic interest that is significantly greater than its stated power to direct activities of the project.

+ References

No definition available.

+ Details

Name:	exc_ProjectsWithSignificantEconomicPower
Namespace Prefix:	exc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

For an unclassified balance sheet, amount of receivables due from an entity that is affiliated with the reporting entity by means of direct or indirect ownership.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of equity, excluding noncontrolling interest, attributable to the equity method investment of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 4
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

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-Paragraph 4
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The proceeds from the sale of an interest in a unit of partnership.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
-Paragraph 14
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

- Definition

Net carrying amount of the assets and liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), when the reporting entity is not the VIE's primary beneficiary.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
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Balance Type:	na
Period Type:	duration

- Details

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- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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Balance Type:
Period Type:

- Details

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- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
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- Details

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Variable Interest Entities Variable Interest Entities - Narrative (Details) $ in Millions	1 Months Ended				12 Months Ended
	Jul. 31, 2017 USD ($)	Nov. 30, 2015	Jun. 30, 2015	Jul. 30, 2014	Dec. 31, 2018 USD ($) VIE project	Dec. 31, 2017 USD ($) VIE	Dec. 31, 2016 USD ($)	Jul. 18, 2014 USD ($)	Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items]
Number of variable interest entities consolidated \| VIE					5	5
Number of variable interest entities not consolidated by equity holders \| VIE					7	7
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net					$ 15
Guarantee obligations maximum exposure					61
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount					15
2015 ESA Investco, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			99.00%
Payment Guarantee [Member] \| CENG [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure									$ 245
Financial Guarantee [Member] \| CENG [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure									165
Equity interest member [Member] \| 2015 ESA Investco, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			90.00%
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net					13
Parental guarantee provided					$ 34
Ownership Percentage Of Consolidated Variable Interest Entities					62.00%
Wind project entities with noncontrolling equity interests \| project					4
Noncontrolling equity interest ownership percentage held by third parties					1.00%
Number of projects with significant economic power \| project					3
Ownership interests in project entities					99.00%
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount					$ 13
Exelon Generation Co L L C [Member] \| ExGen Renewables Holdings, LLC [Member]
Variable Interest Entity [Line Items]
Proceeds from Sale of Interest in Partnership Unit	$ 400
Exelon Generation Co L L C [Member] \| Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage					100.00%
Ownership Percentage Of Consolidated Variable Interest Entities					100.00%
Exelon Generation Co L L C [Member] \| Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Parental guarantee provided					$ 275
Exelon Generation Co L L C [Member] \| CENG [Member]
Variable Interest Entity [Line Items]
Parental guarantee provided					$ 688
Ownership interest					50.01%
Due from Affiliates					$ 196				$ 400
Exelon Generation Co L L C [Member] \| Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage				90.00%
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests					227			$ 85
Exelon Generation Co L L C [Member] \| Equity interest member [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		69.00%
Exelon Generation Co L L C [Member] \| Equity interest member [Member] \| ExGen Renewables Holdings, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	49.00%
Exelon Generation Co L L C [Member] \| Equity interest member [Member] \| Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage				90.00%
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure					16
Atlantic City Electric Company [Member] \| ATF [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE					$ 30	$ 48	$ 60