EXHIBIT 24

MPLX LP POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints Molly R. Benson, Jodi E. Baker, Shane T. Pfleiderer, Elisa D. Watts and
Joel M. Williams (the "Attorneys"), and each of them, as the true and lawful
attorney or attorneys-in-fact, with full power of substitution and revocation,
for the undersigned and in the name, place and stead of the undersigned, in any
and all capacities, to execute, on behalf of the undersigned, (1) any and all
notices pursuant to Rule 144 under the Securities Act of 1933 with respect to
sales of common units or other securities of MPLX LP, including, without
limitation, all notices of proposed sale on Form 144, and (2) any and all
statements or reports under Section 16 of the Securities Exchange Act of 1934
with respect to the beneficial ownership of common units or other securities of
MPLX LP, including, without limitation, all initial statements of beneficial
ownership on Form 3, all statements of changes in beneficial ownership on Form
4, all annual statements of beneficial ownership on Form 5 and all successor or
similar forms, to be filed with the Securities and Exchange Commission, to
execute any and all amendments or supplements to any such notices, statements or
reports, and to file the same, with all exhibits thereto, and other documents in
connection therewith, with the Securities and Exchange Commission, granting to
said Attorney or Attorneys-in-fact, and each of them, full power and authority
to do so and perform each and every act and thing requisite and necessary to be
done in and about the premises (including, without limitation, completing,
executing, delivering and filing a Form ID to apply for electronic filing
codes), as fully and to all intents and purposes as the undersigned might or
could do in person, and hereby ratifying and confirming all that said Attorney
or Attorneys-in-fact, or any of them, or their substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.  The undersigned acknowledges
that the foregoing Attorneys-in-fact, and each of them, in serving in such
capacity at the request of the undersigned, are not assuming any of the
responsibilities of the undersigned to comply with Section 16 of the Securities
Exchange Act of 1934 or any other legal requirement.  This Power of Attorney
shall remain in effect until revoked in writing by the undersigned.


/s/ Carl Kristopher Hagedorn
Carl Kristopher Hagedorn


Date:  1/24/2019