Exhibit 24


                               POWER OF ATTORNEY

   For Executing Forms 3, 4 and 5 Pursuant to Section 16(a) of the Securities
                                  Exchange Act


        Know all by these presents, that the undersigned hereby constitutes and
appoints each of Margaret Austin Wright, Jenelle Chalmers and Mary Croft signing
singly, his/her true and lawful attorney-in-fact to:

          (1) execute for and on behalf of the undersigned Forms 3, 4 and 5 and
              amendments thereto in accordance with Section 16(a) of the
              Securities Exchange Act of 1934 and the rules thereunder;

          (2) do  and  perform  any and  all acts for and  on  behalf of the
              undersigned which may be necessary or desirable to complete the
              execution of any such Form 3, 4 and 5 and the timely  filing of
              such form with the United States Securities and Exchange
              Commission and any other authority; and

          (3) take any other action of any type whatsoever in connection with
              the foregoing which, 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
              his/her discretion.

        The undersigned hereby grants to each such attorney-in-fact full power
and authority to do and perform all and every act and thing whatsoever
requisite, necessary and proper to be done in the exercise of any of the rights
and powers herein granted, as fully to all intents and purposes as such
attorney-in-fact 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 his/her 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 attorney-in-
fact,  in serving in such capacity  at the request  of the undersigned,  are not
assuming  any of the undersigned's responsibilities to comply with Section 16
of the Securities Exchange Act of 1934.

        This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms, 3, 4, and 5 with respect to the
undersigned's  holdings  of and transactions in securities issued by 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 8th day of May 2020.


                                        Signature: /s/ Michael G. Dennis
                                                  ----------------------------

                                        Print Name: Michael G. Dennis
                                                   -----------------------------