Exhibit 99.10

                                POWER OF ATTORNEY

     Each of the undersigned persons hereby constitutes and appoints Douglas L.
Anderson and Paul J. Leighton and each of them severally, as the true and lawful
attorneys-in-fact and agents of such undersigned person, with power to act with
or without the other and with full power of substitution and resubstitution, to
execute in the name, place and stead of such undersigned person, in any and all
capacities, any and all amendments to the Schedule 13D relating to the shares of
common stock, without par value, of Constellation Energy Group, Inc., a Maryland
corporation, filed by each of the undersigned persons, and to which this Power
of Attorney is attached as an Exhibit, and to file the same, with all exhibits
thereto, and all other documents in connection therewith, with the United States
Securities and Exchange Commission, said attorneys-in-fact and agents having
full power and authority to do and perform in the name and on behalf of any and
all of the undersigned persons each and every act and thing requisite and
necessary to be done in the exercise of any of the rights and powers herein
granted as fully and as effectually as the undersigned persons might or could do
in person; and each of the undersigned persons hereby ratifies and confirms all
that said attorneys-in-fact and agents or their substitute or substitutes may
lawfully do or cause to be done by virtue hereof in furtherance of such
foregoing purposes.

     This Power of Attorney shall remain in full force and effect with respect
to an undersigned person until revoked by such undersigned person in a signed
writing delivered to the foregoing attorneys-in-fact and agents.

     IN WITNESS WHEREOF, the undersigned have executed this Power of Attorney as
of February 6, 2009.



                           MidAmerican Energy Holdings Company


                           By:     /s/ Douglas L. Anderson
                                   ---------------------------------------------
                                   Name:  Douglas L. Anderson
                                   Title: Senior Vice President, General
                                          Counsel and Corporate Secretary


                           MEHC Investment, Inc.


                           By:     /s/ Douglas L. Anderson
                                   ---------------------------------------------
                                   Name:  Douglas L. Anderson
                                   Title: Vice President and Secretary


                           Berkshire Hathaway Inc.


                           By:     /s/ Marc D. Hamburg
                                   ---------------------------------------------
                                   Name:  Marc D. Hamburg
                                   Title:    Senior Vice President


                           /s/ Warren E. Buffett
                           -----------------------------------------------------
                           Warren E. Buffett