Represents the total number of members on board.

Name:	ceg_DivestitureRightToAppointMembersOnBoardNumberOfMembersOnBoard
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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of members on board to be appointed on account of divestiture rights sold.

+ Details

Name:	ceg_DivestitureRightToAppointMembersOnBoardSoldNumberOfMembers
Namespace Prefix:	ceg
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the pre-tax gain on change in accounting method due to reclassification of entity's investment income from accumulated other comprehensive income to earnings.

+ Details

Name:	ceg_GainOnReclassifiedInvestmentIncomeDueToChangeOfAccountingMethodBeforeTax
Namespace Prefix:	ceg
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The value of the consideration received in cash for selling an asset or business through a noncash (or part noncash) transaction.

+ Details

Name:	ceg_NoncashOrPartNoncashDivestitureAmountOfConsiderationReceivedInCash
Namespace Prefix:	ceg
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of common shares received for consideration for selling an asset or business through a noncash (or part noncash) transaction.

+ Details

Name:	ceg_NoncashOrPartNoncashDivestitureAmountOfConsiderationReceivedThroughCommonStock
Namespace Prefix:	ceg
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of member interests sold by the reporting entity through a noncash (or part noncash) transaction.

+ Details

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Namespace Prefix:	ceg
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents additional shares to be obtained on conversion of warrants.

+ Details

Name:	ceg_NoncashOrPartNoncashDivestituresAcquisitionOfSharesOnConversionOfWarrants
Namespace Prefix:	ceg
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the underlying power generation capacity of the entities acquired.

+ Details

Name:	ceg_UnderlyingPowerGenerationCapacityOfAcquiredEntities
Namespace Prefix:	ceg
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

- Definition

The gain (loss) resulting from the sale of a disposal group that is not a discontinued operation. It is included in income from continuing operations before income taxes in the income statement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6390789&loc=d3e2443-110228

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 144

-Paragraph 47

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 144

-Paragraph 37, 45

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

Divestitures (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		1 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Aug. 31, 2011 Constellation Energy Partners LLC Member MemberInterest	Sep. 30, 2011 Constellation Energy Partners LLC	Dec. 31, 2010 Quail Run Energy Center mW
Definitive purchase and sale agreement
Number of members on board to be appointed on account of divestiture rights sold					2
Total number of members on board					5
Number of Class B member interests sold (in units)					3,100,000
Cash received on divestiture					$ 6.6
Number of common shares of PostRock to be received on divestiture (in shares)					1,000,000
Shares to be acquired on conversion of warrants (in shares)					673,822
Pre-tax gain on divestitures	23.0	38.3	23.0	43.5	11.4
Underlying power generation capacity of acquired entities (in megawatts)							550
Pre-tax gain of reclassified investment income from accumulated other comprehensive income to earning						$ 11.6