POWER OF ATTORNEY
       For Executing Forms 3, 4 and 5, Form 144 and Schedules 13D and 13G

     Known by all these present, that the undersigned hereby constitutes and
appoints each of Matthew J. Meloy, Jennifer R. Kneale and Regina L. Gregory, or
any of them signing singly, and with full power of substitution, the
undersigned's true and lawful attorney-in-fact to:

(1)  execute for and on behalf of the undersigned (a) Forms 3, 4 and 5
     (including any amendments, corrections, supplements or other changes
     thereto) in accordance with Section 16(a) of the Securities Exchange Act of
     1934, as amended (the "Exchange Act"), and the rules thereunder, (b) Form
     144 and (c) Schedules 13D and 13G (including any amendments, corrections,
     supplements or other changes thereto) in accordance with Sections 13(d) and
     13(g) of the Exchange Act and the rules thereunder, but only to the extent
     each such form or schedule relates to the undersigned's beneficial
     ownership of securities of Targa Resources Corp. or any of its
     subsidiaries;

(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 Form 3, 4 or
     5, Form 144 or Schedule 13D or 13G (including any amendments, corrections,
     supplements or other changes thereto) and timely file such Forms or
     Schedules with the Securities and Exchange Commission and any stock
     exchange or quotation system, self-regulatory association or any other
     authority, and provide a copy as required by law or advisable to such
     persons as the attorney-in-fact deems appropriate; and

(3)  take any other action of any type whatsoever in connection with the
     foregoing that, in the opinion of each such attorney-in-fact, may be of
     benefit to, in the best interest of, or legally required of the
     undersigned, it being understood that the documents executed by the
     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 the attorney-in-fact may approve in the attorney-in-fact's discretion.

     The undersigned hereby grants to each attorney-in-fact full power and
authority to do and perform all 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 the attorney-in-fact, or the attorney-
in-facts substitutes or substitute, 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, and their
substitutes, in serving in such capacity at the request of the undersigned, are
not assuming (nor is Targa Resources Corp. assuming) any of the undersigned's
responsibilities to comply with Section 16 of the Exchange Act.

     The undersigned agrees that each such attorney-in-fact may rely entirely on
information furnished orally or in writing by or at the direction of the
undersigned to the attorney-in-fact. The undersigned also agrees to indemnify
and hold harmless Targa Resources Corp. and each such attorney-in-fact against
any losses, claims, damages or liabilities (or actions in these respects) that
arise out of or are based upon any untrue statements or omissions of necessary
facts in the information provided by or at the direction of the undersigned, or
upon the lack of timeliness in the delivery of information by or at the
direction of the undersigned, to such attorney-in-fact for purposes of
executing, acknowledging, delivering or filing Forms 3, 4 or 5, Form 144 or
Schedule 13D or 13G (including any amendments, corrections, supplements or other
changes thereto) with respect to the undersigned's holdings of and transactions
in securities issued by Targa Resources Corp. and agrees to reimburse Targa
Resources Corp. and such attorney-in-fact on demand for any legal or other
expenses reasonably incurred in connection with investigating or defending
against any such loss, claim, damage, liability or action.

     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, Form 144 and
Schedules 13D and 13G (including any amendments, corrections, supplements or
other changes thereto) with respect to the undersigned's holdings of and
transactions in securities issued by Targa Resources Corp., unless earlier
revoked by the undersigned in a signed writing delivered to the foregoing
attorneys-in-fact. This Power of Attorney does not revoke any other powers of
attorney that the undersigned has previously granted concerning the matters
described herein.

     IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be
executed as of the date written below.

                                      /s/ Regina L. Gregory
                                      ---------------------
                                      Regina L. Gregory

                                      March 10, 2020