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Investment in Constellation Energy Nuclear Group, LLC (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)	1.00%
Impact Of Transactions Under Agreements [Abstract]
Increase (Decrease) in earnings	$ 48.00	$ 9.00	$ 6.00
Amortization of energy contract assets and liabilities	1,110.00
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Purchase of nuclear output by EDF (as a percent)	49.99%
Impact Of Transactions Under Agreements [Abstract]
Increase (Decrease) in earnings	1,702.00	1,161.00	3,102.00
Amortization of energy contract assets and liabilities	1,110.00
Exelon Generation Co L L C [Member] \| CENG [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)	50.01%
Basis difference in investment in CENG	$ 204.00

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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