Derivative Instruments (Details 4) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Derivatives, Fair Value
Gross fair value of derivative contracts containing a credit-risk related contingent feature	$ 3,100,000,000	$ 4,600,000,000
Offsetting fair value of in-the-money contracts under master netting arrangements	(2,600,000,000)	(3,700,000,000)
Net fair value of derivative contracts containing a credit-risk related contingent feature	500,000,000	900,000,000
Cash collateral and letters of credit, collateral posted	400,000,000	700,000,000
Contingent collateral obligation	100,000,000	100,000,000
Cash collateral posted	2,500,000	600,000
Letters of credit, collateral posted	$ 412,400,000	$ 656,900,000
Concentration of credit risk, percentage (as a percent)	14.00%
Counterparties exceeding the maximum credit exposure trigger percentage, number	1

The aggregate amount of cash collateral and letters of credit already posted, at the end of the reporting period, as collateral for out-of-the-money derivative instruments with credit-risk related contingent features.

Name:	ceg_CashCollateralAndLettersOfCreditAlreadyPostedAggregateFairValue
Namespace Prefix:	ceg
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of counterparties exceeding the maximum credit exposure trigger percentage.

+ Details

Name:	ceg_ConcentrationOfCreditRiskCounterpartiesExceedingMaximumCreditExposureTriggerPercentageNumber
Namespace Prefix:	ceg
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage credit exposure of the entity to any single obligor or counterparty (including a collection of counterparties based in a single country other than the United States) that is considered to be a significant concentration of credit risk.

+ Details

Name:	ceg_ConcentrationOfCreditRiskExposurePercentage
Namespace Prefix:	ceg
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the gross fair value of out-of-the money derivative contracts containing credit-risk related contingent features that are not fully collateralized by posted cash collateral on an individual, contract-by-contract basis ignoring the effects of master netting arrangements.

+ Details

Name:	ceg_FairValueOfDerivativeWithCreditRiskRelatedContingentFeatureGross
Namespace Prefix:	ceg
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate amount of letters of credit already posted, at the end of the reporting period, as collateral for out-of-the-money derivative instruments with credit-risk related contingent features.

+ Details

Name:	ceg_LettersOfCreditCollateralAlreadyPostedFairValueDerivativeLiabilities
Namespace Prefix:	ceg
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44D
-Subparagraph c

+ Details

Name:	us-gaap_AdditionalCollateralAggregateFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44D
-Subparagraph c

+ Details

Name:	us-gaap_CollateralAlreadyPostedAggregateFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount as of the balance sheet date of the fair value of derivative assets that in accordance with the entity's accounting policy was offset against an obligation to return cash collateral under a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FIN39-1
-Paragraph 10B
-Subparagraph b

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain or loss on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44D
-Subparagraph b

+ Details

Name:	us-gaap_DerivativeNetLiabilityPositionAggregateFairValue
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.

+ Details

Name:	us-gaap_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration