Derivative Financial Instruments - Net Credit Exposure by Type of Counterparty (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Cash collateral held	$ 69exc_CashCollateralHeld
Letters of credit held	16exc_LettersOfCreditHeld
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral held	77	206
Letters of credit held	24	34
Exelon Generation Co L L C [Member] \| Net Exposure [Member]
Derivative [Line Items]
Financial institutions	295
Investor-owned utilities, marketers, power producers	958
Energy cooperatives and municipalities	862
Other	17
Total	$ 2,132

Cash collateral held related to credit risk.

No definition available.

Name:	exc_CashCollateralHeld
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

- 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

- Definition

+ References

No definition available.

+ Details

Name:	exc_InvestorOwnedUtilitiesMarketersAndPowerProducersCreditRiskExposure
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

- Definition

+ References

No definition available.

+ Details

Name:	exc_OtherCreditRiskExposure
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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=7476318&loc=SL5708775-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Credit Derivative

-URI http://asc.fasb.org/extlink&oid=6854095

+ Details

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

- Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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