Goodwill (Details) (USD $) In Millions, unless otherwise specified			6 Months Ended
Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Commonwealth Edison Co [Member]
Goodwill, Impaired [Abstract]
Percentage decrease in fair value			10.00%
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 2,625	$ 2,625	$ 2,625
Goodwill, ending balance	$ 2,625	$ 2,625	$ 2,625

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

+ Details