Intangible Assets (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Goodwill [Line Items]
Goodwill, beginning balance	$ 2,625,000,000	$ 2,625,000,000
Goodwill, ending balance	2,625,000,000	2,625,000,000
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill, beginning balance	2,625,000,000	2,625,000,000
Goodwill, ending balance	$ 2,625,000,000	$ 2,625,000,000

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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+ Details