TERMINATION AGREEMENT

Exhibit 2.1

TERMINATION AGREEMENT

TERMINATION AGREEMENT (this “Agreement”) dated as of December 17, 2008 by and among MIDAMERICAN ENERGY HOLDINGS COMPANY, an Iowa corporation (“MidAmerican”), MEHC INVESTMENT, INC., a South Dakota corporation and a wholly owned subsidiary of MidAmerican (“MEHC Investment”), MEHC MERGER SUB INC., a Maryland corporation and a wholly owned subsidiary of MidAmerican (“Merger Sub” and, together with MidAmerican and MEHC Investment, the “MidAmerican Parties”), CONSTELLATION ENERGY GROUP, INC., a Maryland corporation (“Constellation”), CER GENERATION II LLC (“CER LLC”), CONSTELLATION POWER SOURCE GENERATION, INC. (“Constellation Power”) and ÉLECTRICITÉ DE FRANCE INTERNATIONAL, SA, a société anonyme organized under the laws of France (“EDFI”).

WHEREAS, MidAmerican, Merger Sub and Constellation entered into an Agreement and Plan of Merger dated as of September 19, 2008 (the “Merger Agreement”) providing, upon the terms and subject to the conditions thereof, for Merger Sub to be merged with and into Constellation (the “Merger”);

WHEREAS, capitalized terms used and not defined herein shall have the meanings ascribed to such terms in the Merger Agreement;

WHEREAS, Constellation has previously filed Articles Supplementary with the State Department of Assessments and Taxation of Maryland (as corrected by the Certificate of Correction filed on November 26, 2008, the “Series A Articles Supplementary”) that designated certain preferences, conversion and other rights of Series A Convertible Preferred Stock of Constellation (the “Series A Preferred Stock”);

WHEREAS, MidAmerican and Constellation entered into a Stock Purchase Agreement dated as of September 19, 2008 (the “MidAmerican Stock Purchase Agreement”) pursuant to which MidAmerican (through MEHC Investment) purchased 10,000 shares of Series A Preferred Stock from Constellation on September 22, 2008;

WHEREAS, pursuant to the terms of the Series A Articles Supplementary and the Limited Waiver between MidAmerican and Constellation dated November 23, 2008 (the “Limited Waiver”), upon the occurrence of a Conversion Event (as defined in the Series A Articles Supplementary), and subject to the receipt of all required regulatory approvals, the Series A Preferred Stock will be automatically converted into (A) 35,679,215 shares (the “Conversion Share Amount”) of common stock of Constellation (the “Common Stock”) and (B) Senior Notes with an original aggregate principal amount equal to the aggregate Stated Value of the Series A Preferred Stock (each as defined in the Series A Articles Supplementary);

WHEREAS, in the event Constellation has not received all regulatory approvals required for the issuance of the Conversion Share Amount upon a Conversion Event, the Series A Articles Supplementary and Limited Waiver provide that Constellation shall make a cash payment to the holder of Series A Preferred Stock in lieu of the issuance of the shares of Common Stock that are otherwise due to the holder in an amount equal to (i) the number of shares of the Common Stock issuable to the holder and not issued multiplied by (ii) $26.50, subject to certain adjustments;

WHEREAS, MidAmerican, Merger Sub, Constellation, CER LLC and Constellation Power entered into two Put Agreements dated as of November 6, 2008 (the “MidAmerican Put Agreements” and, together with the Merger Agreement, the MidAmerican Stock Purchase Agreement and

the Confidentiality Agreement, the “Specified MidAmerican Agreements”) providing, upon the terms and subject to the conditions thereof, Constellation with a put option to sell certain assets to MidAmerican;

WHEREAS, in connection with a Takeover Proposal made by EDFI, the board of directors of Constellation has notified MidAmerican that in the absence of proposed revisions to the terms of the Merger Agreement or another proposal by MidAmerican contemplated by Section 7.8(d)(iii) of the Merger Agreement, it would withdraw the Company Board Recommendation pursuant to Section 7.8(d)(iii) of the Merger Agreement;

WHEREAS, in lieu of MidAmerican exercising its rights under Sections 7.4 and 7.8(d)(iii) of the Merger Agreement, the MidAmerican Parties and Constellation have agreed to terminate the Specified MidAmerican Agreements pursuant to the terms and subject to the conditions hereof;

WHEREAS, simultaneously with the termination of the Specified MidAmerican Agreements, (i) Constellation, EDFI, Constellation Energy Nuclear Group, LLC, a Maryland limited liability company and a wholly owned subsidiary of Constellation (“CENG”) and EDF Development, Inc., a Delaware corporation and a wholly owned subsidiary of EDFI (“EDFD”), intend to execute a Master Put Option and Membership Interest Purchase Agreement of even date herewith, a copy of which is attached hereto as Exhibit A (the “Master Agreement”), providing, upon the terms and conditions thereof, for the purchase by EDFD from Constellation of a 49.99% membership interest in CENG and the grant of put options to Constellation in respect of specified assets, (ii) Constellation and EDFD intend to execute a Stock Purchase Agreement of even date herewith, a copy of which is attached hereto as Exhibit B (the “EDF Stock Purchase Agreement”), providing, upon the terms and conditions thereof, for the purchase by EDFD of shares of Series B Preferred Stock of Constellation with an aggregate stated value of $1,000,000,000, and (iii) Constellation and EDFI intend to enter into (and/or to cause one or more of their respective subsidiaries to enter into) certain agreements related to the Master Agreement and the Stock Purchase Agreement (the transactions contemplated by the Master Agreement, the EDF Stock Purchase Agreement and such related agreements, the “EDFI Transactions”);

WHEREAS, the parties hereto desire to confirm certain actions required or deemed appropriate in connection with the termination of the Specified MidAmerican Agreements, including the payment by Constellation of amounts owed pursuant to the Merger Agreement and the Articles Supplementary and the issuance by Constellation of Common Stock pursuant to the Articles Supplementary upon the termination of the Merger Agreement and the mutual releases of any and all claims arising under or relating to the Specified MidAmerican Agreements;

WHEREAS, the board of directors of Constellation has taken all actions necessary to render any applicable state anti-takeover law or similar law inapplicable to the issuance of shares of Common Stock contemplated herein; and

WHEREAS, the MidAmerican Parties, EDFI and Constellation believe that it is in their respective best interests and in the best interests of their respective stockholders that any uncertainty or disputes with respect to the Merger be resolved as promptly as practicable.

NOW THEREFORE, in consideration of the foregoing and the mutual agreements herein set forth, and for other good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, the parties hereto do hereby agree as follows:

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IN WITNESS WHEREOF, this Agreement has been duly executed by the parties hereto all as of the day and year first above written.

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