POWER OF ATTORNEY

        Know all by these presents, that the undersigned hereby constitutes and
appoints each of Kathryn McNamara Corley, Christopher Greene and Simon Halfin,
signing singly, the undersigned's true and lawful attorney-in-fact to:

        (1)     execute for and on behalf of the undersigned, all reports to be
        filed by the undersigned pursuant to Section 16(a) of the Securities
        Exchange Act of 1934, as amended (the "Exchange Act") and the rules
        promulgated thereunder (including Forms 3, 4, and 5 and any successor
        forms) (the "Section 16 Reports") with respect to the equity securities
        of Discover Financial Services (the "Company");

        (2)     do and perform any and all acts for and on behalf of the
        undersigned that may be necessary or desirable to complete and execute
        any such Section 16 Report, complete and execute any amendment or
        amendments thereto, and file such report with the United States
        Securities and Exchange Commission and any stock exchange of similar
        authority; and

        (3)     take any other action of any type whatsoever in connection with
        the foregoing that, in the opinion of such attorney-in fact, may be of
        benefit to, in the best interest of, or legally required by, the
        undersigned, it being understood that the documents executed by such
        attorney-in-fact on behalf of the undersigned pursuant to this Power of
        Attorney shall be in such form and shall contain such terms and
        conditions as such attorney-in-fact may approve in such
        attorney-in-fact's discretion.

        The powers granted above may be exercised by each such attorney-in-fact
on behalf of the undersigned, individually, and on behalf of the undersigned in
any fiduciary or representative capacity in which the undersigned may be acting.

        The undersigned hereby grants to each such attorney-in-fact full power
and authority to do and perform any and every act and thing whatsoever
requisite, necessary, or proper to be done in the exercise of any of the rights
and powers herein granted, as fully to all intents and purposes as the
undersigned might or could do if personally present, with full power of
substitution or revocation, hereby ratifying and confirming all that such
attorney-in-fact, or such attorney-in-fact's substitute or substitutes, shall
lawfully do or cause to be done by virtue of this Power of Attorney and the
rights and powers herein granted. The undersigned acknowledges that the
foregoing attorneys-in-fact, in serving such capacity at the request of the
undersigned, are not assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of the Exchange Act.

        This Power of Attorney shall be effective as of the date set forth below
and shall continue in full force and effect until the undersigned is no longer
required to file Section 16 Reports with respect to the equity securities of the
Company, unless earlier revoked by the undersigned in a signed writing delivered
to the foregoing attorneys-in-fact.

        IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this 25th day of June, 2007.

Signature:  /s/ David W. Nelms
            ----------------------------

Print Name: David W. Nelms