Accounts Receivable (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts Notes And Loans Receivable Net Current [Abstract]
Unbilled revenues	$ 1,418.00	$ 902.00
Allowance for uncollectible accounts	(293.00)	(199.00)
Accounts Receivable Additional Disclosures [Abstract]
Accounts receivable, pledged under accounts receivable agreement	225.00
Gross Accounts Receivable Pledged as Collateral	289.00	346.00
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables	18.00	21.00
Exelon Generation Co L L C [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Unbilled revenues	859.00	493.00
Allowance for uncollectible accounts	(84.00)	(29.00)
Commonwealth Edison Co [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Unbilled revenues	213.00	246.00
Allowance for uncollectible accounts	(70.00)	(78.00)
PECO Energy Co [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Unbilled revenues	164.00	163.00
Allowance for uncollectible accounts	(99.00)	(92.00)
Accounts Notes And Loans Receivable Net Current Footnotes [Abstract]
Current financing receivable allowance for credit losses	7.00	8.00
Accounts Receivable Additional Disclosures [Abstract]
Accounts receivable, pledged under accounts receivable agreement	225.00
Gross Accounts Receivable Pledged as Collateral	289.00	329.00
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(15.00)	(17.00)
PECO Energy Co [Member] \| Low Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(1.00)	(1.00)
PECO Energy Co [Member] \| Medium Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(3.00)	(3.00)
PECO Energy Co [Member] \| High Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(11.00)	(13.00)
Baltimore Gas and Electric Company [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Unbilled revenues	182.00	194.00
Allowance for uncollectible accounts	$ (40.00)	$ (37.00)

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The current valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible relating to installment plans.

+ References

No definition available.

+ Details

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- Definition

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5074-111524

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(1)

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- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Article 5

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of finance receivables which are owned but transferred to serve as collateral for the payment of the related debt obligation, primarily a secured borrowing or repurchase agreement, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 17

-Subparagraph a(2)

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)

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- Definition

The sum of the fair values, as of the date of each statement of financial position presented, of assets which are owned but transferred to serve as collateral for the payment of debt obligations, primarily secured borrowings, repurchase agreements or other current or potential obligations, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6467456&loc=d3e113888-111728

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 15

-Subparagraph a

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- Definition

Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

+ References

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

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 43

-Section A

-Paragraph 4, 21

-Chapter 11

-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.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 912

-SubTopic 310

-Section 45

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-URI http://asc.fasb.org/extlink&oid=6471842&loc=d3e55302-109406

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